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. 2020 Jan 6;5(2):1098–1108. doi: 10.1021/acsomega.9b03260

Catalytic Reclamation of Silver Present in Photographic Waste Using Magnetically Separable TiO2@CuFe2O4 Nanocomposites and Thereof Its Use in Antibacterial Activity

Vrushali B Shevale 1, Ananta G Dhodamani 1, Sagar D Delekar 1,*
PMCID: PMC6977080  PMID: 31984266

Abstract

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In the present investigation, the silver present in photographic waste is reclaimed catalytically using magnetically separable TiO2@CuFe2O4 nanocomposites (NCs), and further, the recovered silver nanoparticles [Ag(0) NPs] are tested against the representative bacteria for the antibacterial activity. Initially, a series of the different composites between TiO2 nanoparticles and CuFe2O4 nanoparticles are synthesized by a sol–gel “ex situ” method to enhance the catalytic activity of bare nanomaterials toward the visible region of the electromagnetic spectrum. X-ray diffraction reveals the presence of characteristic patterns for the tetragonal structure in the bare materials or TiO2@CuFe2O4 NCs; however, the dominance in the phase as well as intensity of the respective XRD reflections in the NCs is observed according to the content of TiO2 or CuFe2O4 in the NCs. Field-emission electron microscopic images show the uniform spherical particles for the representative TiO2@CuFe2O4 NCs, which is also confirmed through the HRTEM images. The magnetically separable behavior of the representative TiO2@CuFe2O4 NCs is confirmed through the VSM measurements, which also shows the superparamagnetic properties due to the S-shaped nature of the hysteresis loop. Thereafter, a photoconversion reaction of Ag(I) ions to Ag(0) NPs as a model reaction is carried out using the different TiO2@CuFe2O4 NCs under visible light irradiation, and hence, the higher catalytic recovery of Ag(0) NPs is observed for a composite containing 10 wt % TiO2 and 90 wt % CuFe2O4 than that of other NCs or the bare one alone. The optimized protocol of the model reaction is adopted for reclaiming Ag(0) NPs from photographic waste. The progress of the catalytic reclamation reaction is monitored using UV–visible, and then sizes of the recovered Ag(0) NPs are confirmed through the HRTEM images. Thereafter, the recovered Ag(0) NPs are tested for complete photoinactivation of Escherichia coli bacteria within 120 min.

Introduction

Medical practices and the film industry have been extensively using photographic or X-ray films for different purposes, which are developed with photosensitive materials.1 During the development of these films, silver-containing waste is generated usually. This photographic waste is in the form of a typical black and white solution containing silver ions with other ions such as halides, sulfite, thiosulfate, acetates, etc., and it is discharged into the environment. Due to such discharge into the environment, the effluents containing silver may cause toxic exposure to aquatic organisms. Also, literature studies revealed that excessive silver in the food chain of humans has noticeable toxicity against the cell lines of human beings, and hence it may cause kidney or liver damage, skin or eye irritation, etc.2−5 Along with its toxicity to living organisms, silver is a precious element used in ornaments, alloys, electrical contacts, batteries, antibacterial agents, etc. Hence, silver discharge is one of the issues in front of investigators or the government, which is to be solved for gaining not only the good health of human beings but also an economical status of a country. Therefore, ease of the recovery of silver from photoprocessing waste is in dire need for further research endeavors. Various methods have been established to recover silver in photographic waste such as use of a metallic replacement,6 ion exchange,7 electrolytic plating,8 and chemical precipitation techniques.9 However, these methods are suffering from the various constraints during the actual silver recovery from waste. The chemical precipitation technique is used commonly by the companies; however, the tedious protocols and the availability of costly processing equipment are the hindrances of such a method. Moreover, use of a metallic replacement is also no longer effective due to the loss of the silver-based sludge after refining. In electrolytic recovery, several factors such as the potential of the fixer solution, agitation, current density, electrode material, solution filtration, pH of the solution, etc. are optimized through the number of attempts for silver recovery at low concentrations (<100 mg/L).10 In the case of ion-exchange methods, silver is removed with alkaline solutions of KCN or Na2S2O7 as a complexing agent, but they use more water as well as a tedious experimental setup for separating the mobile phase and stationary phase to recover silver very efficiently using a column. Besides, the cost and maintenance of the ion-exchange method are also high compared to others. Therefore, these protocols have certain pros and cons concerning each method for recovering silver from waste. Hence, in the present context, the green, easy, and sustainable nanocomposite (NC)-based protocol is reported for reclaiming the Ag(I) ion present in photographic waste to nanocrystalline Ag(0).

For converting the silver ion to elemental silver, various reducing agents such as NaBH4, citrate, borohydride, and ascorbate11−13 are used. In comparison to these reductants, the NCs are promising in respective silver conversions, which are due to their higher surface areas, better optoelectrical properties resulting in a strong oxidant/reductant nature, enhancement in catalytic properties, and easy separation of the catalysts from the reaction mixture. Therefore, the investigators have used various NCs for this conversion as well. Wei et al. reported the formation of Ag NPs from contaminated water containing Ag(I) ions using Fe3O4@microbial extracellular polymeric substance (EPS) NCs, but the overall synthetic route is not easier due to the anchoring between the different components of the catalysts.14 Similarly, reduction of Ag(I) ions by amino acid tyrosine at alkaline pH is reported, but this method requires continuous monitoring of the reaction for temperature control.15 Ag(0) NPs are also formed in situ on the surface of magnetic graphene oxide using polyethylenimine as a reducing as well as stabilizing agent, and hence the obtained composites are used for selective enrichment of glycopeptides. The overall selectivity of this protocol is not up to the mark in comparison to the other composites, which could be due to the multicomponent system affecting the applications.16 Similarly, Luo et al. recovered silver from wastewater using polymeric-based Fe3O4–SiO2–TiO2 composites; however, the recovered Ag is strongly adsorbed on the catalysts used.17 Huang et al. used nanosorbents of poly[aniline(AN)-co-5-sulfo-2-anisidine(SA)] for the removal of Ag(I) ions to Ag nanocrystals. This is possible due to the fact that the functional groups of the polymer are directly used to recover and separate precious Ag from wastewaters; however, the new Ag polymer nonabsorbent is formed, and hence its further applicability is limited.18 From these various reports, bare Ag(0) NP recovery from photographic waste is one of the very common challenging tasks with the use of NCs due to various constraints. With the motivation of Ag(0) NP recovery from waste as well as overcoming the various experimental hindrances of earlier reported research endeavors, we have designed the protocol for the recovery of Ag(0) NPs from photographic waste using magnetically recoverable TiO2@CuFe2O4 (TCU) NCs, and hence the recovered colloidal Ag(0) NPs are further utilized for antibacterial activity against the representative bacteria.

In the present context, particularly, TCU NCs have been focused on Ag(0) NP recovery from photographic waste under visible light irradiations. This is because it is well known that TiO2 is the best photocatalyst and also acts as an optically active material19 and CuFe2O4 is an inverse spinel ferrite having better magnetization in the presence of a magnetic field and also having an optical band gap toward the visible–NIR region of the electromagnetic spectrum.20 The combination of these effective components leads to the enhancements in the optical, electrical properties due to the proper charge trapping between the densities of states for retarding the electron–hole recombination rates,21 mixing of band levels covering a wide optical coverage, formation of a heterostructure leading to effective charge separation,22 formation of charge carriers, and availability of more active sites for better catalytic activity.23 In these connections, fewer studies related to the potential applications of TiO2@CuFe2O4 have been found in the literature. However, similar to our desired heterojunction composites, investigators used the different composites of TiO2 with other ferrites. Bechelany et al. reported photodegradation of methylene blue in visible light irradiation by combination of a spinel ferrite with TiO2 for enhancing the efficiency of the photodegradation reaction.24 Wang et al. also synthesized TiO2–ZnFe2O4 in nanotube arrays for improving the photoresponse properties, and then these NCs were efficiently used in various applications such as water splitting, solar energy utilization, and degradation of waste water.25 The enhancement in photoelectrochemical performance of CoFe2O4-sensitized TiO2 nanotubes was 30 times higher than that of bare TiO2 due to proper charge separation of free radicals in the visible region.26 The hydrogen generation from methanol/water splitting was reported using a NiFe2O4@TiO2 core@shell structure, which has 10 times higher catalytic activity than that of bare NiFe2O4 and TiO2.27 Based on these investigations, it is realized that the composites of TiO2 with CuFe2O4 would result in the enhancement of the optoelectrical properties of the NCs for efficient catalytic conversion of the Ag(0) NP recovery from waste. Therefore, in the present investigations, different compositions of TCU have been prepared, and thereafter these NCs are used for conversion of Ag(I) ions using visible light irradiation. Then, the optimized protocol is adopted for recovering Ag(0) NPs from photographic waste.28 Thereafter, the recovered Ag(0) NPs are tested against Escherichia coli (E. coli) bacteria.

Results and Discussion

The thermal change of an “as-prepared” hydroxo-copper precursor is studied using thermogravimetric analysis (TGA). Figure 1 shows the thermogram of CU from ambient to 1000 °C in an air atmosphere. The first weight loss up to 0.9% at ∼178 °C is observed due to the elimination of physically adsorbed water molecules from the compound. The second drastic weight loss of 4.6% in the TGA curve from 178 to 400 °C is attributed to the removal of coordinated water as well as organic residues. Moreover, the third change in mass loss from 400 to 500 °C is due to subsequent oxidative decomposition of the precursor with the removal of organic moieties in crystalline CU.29 Taking into account these observations, the compound has been calcinated at 500 °C at room temperature.

Figure 1.

Figure 1

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TGA thermogram of the “as-prepared” hydroxo-copper precursor sample.

X-ray diffraction patterns of bare TiO2, CU, and the representative TCU composites indicate the nanocrystalline nature of all the materials, which are shown in Figure 2. The XRD pattern of TiO2 consists of the characteristic reflections corresponding to the tetragonal structure of TiO2. These characteristic diffraction peaks at 25.36°, 37.94°, and 47.92° indexed to (101), (004), and (200) planes, respectively, completely match with standard XRD patterns (JCPDS no. 84-1285) of anatase TiO2.

Figure 2.

Figure 2

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X-ray diffraction patterns of (a) bare TiO2, (b) TCU2 NCs, (c) bare CU, and (d) TCU4 NCs.

In the case of CU, the XRD pattern displays reflections at 30.06°, 35.99°, and 41.70° corresponding to (200), (211), and (004) planes, respectively, confirming the presence of the tetragonal spinel-type structure of CU. This is in good agreement with the standard XRD pattern (JCPDS no. 00-034-0425). In these patterns, other impurity peaks are not observed.30,15 In the case of TCU NCs shown, the characteristic diffraction peaks of tetragonal anatase TiO2 and spinel CU are observed. Both bare and TCU-based NCs show a tetragonal crystal structure. In the TCU NCs with a higher content of TiO2, the characteristic reflections of TiO2 are dominant, while the reflections of CU are more intense, which have a maximum percentage of CU. It is also seen that decreasing of the peak intensity of NCs is observed after the incorporation of TiO2 and CU compared to that of bare TiO2 or bare CU materials.

The crystallographic parameters of the bare and NCs are shown in Table 1. The crystallite size of TiO2 either in its bare or NC form is observed in the range of 10 to 13 nm, while CU is in the range of 11 to 12 nm.

Table 1. Structural Parameters and Optical Energy Band Gaps of Bare TiO2, Bare CU, and Their Representative NCs.

  observed d values (Å)
 lattice parameters (Å)
 crystallite size (nm)
  
composites TiO2 CU TiO2 CU TiO2 CU prominent crystal system
TiO2 3.507   a = 3.76; c = 9.48   10.77   tetragonal
2.372
1.893
TCU2 3.503   a = 3.76; c = 9.44   12.89   tetragonal
2.368
1.885
TCU4   2.954   a = 5.90; c = 8.60   11.46 tetragonal
2.626
2.151
TCU5   2.978   a = 5.94; c = 8.64   11.53 tetragonal
2.515
2.165
CU   2.972   a = 5.84; c = 8.63   11.84 tetragonal
2.493
2.163
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Transmission electron microscopy (TEM) is useful for studying the morphology as well as the particle size of samples. Figure 3 consists of TEM images of bare CU and TCU4 NCs. Both of the materials show a spherical nature with a compact arrangement of particles, and the particle size of the samples is observed to be within 10 to 13 nm.

Figure 3.

Figure 3

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HRTEM images of (a) bare CU and (c) TCU4 NCs. Lattice fringes with SEAD patterns of (b) bare CU and (d) TCU4 NCs.

High-resolution TEM images of bare CU and TCU NCs show the well-defined crystal fringes, and the difference between the successive layers matches well the d spacing value of the (211) reflections of both samples. The selected-area electron diffraction (SEAD) of bare CU exhibits a well-defined ring structure confirming the crystalline nature of CU; however, in the TCU4 NCs, low-intensity diffuse rings are observed (Figure 3b,d) due to their compositions with TiO2. It is concluded that the well-defined crystalline nature of CU NPs is decreased in the NCs. The lattice fringe widths of bare CU and TCU4 NCs are 2.50 and 2.51 Å, respectively, which matches the d spacing values of the respective reflections of the samples.

Figure 4a,c,e shows the FESEM images of TiO2, bare CU, and representative TCU4 NCs, respectively, and those of TCU2 NCs are shown in the Supporting Information, Figure S1. All these materials show the uniform distribution of spherically shaped particles with agglomeration between the neighboring particles. The grain size obtained from FESEM for the samples is observed in the range of 11 to 12 nm, which matches the crystallite size of XRD analysis. The elemental dispersive X-ray analysis (EDAX) plot of the representative samples is shown in Figure 4b,d,f. EDAX spectra of the respective TiO2, bare CU, and TCU4 NCs show the characteristic peaks of Ti, Cu, Fe, and O only in their patterns revealing the presence of these elements. Table 2 shows that the theoretical and experimental percentages of Ti, Cu, Fe, and O present in TiO2, CU, and TCU4 are in good agreement with each other.

Figure 4.

Figure 4

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FESEM images of (a) TiO2, (c) bare CU, and (e) TCU4 NCs and EDAX patterns of (b) TiO2, (d) bare CU, and (f) TCU4 NCs.

Table 2. Elemental Compositions of TiO2, Bare CU, and TCU4 NCs.

  theoretical values (%)
 experimental values (%)
compositions Ti Cu Fe O Ti Cu Fe O
TiO2 33.3     66.6 31.5     61.4
bare CU   14.30 28.57 57.12   13.95 27.60 40.42
TCU4 5.98 23.90 21.00 49.20 4.72 21.80 20.14 47.18
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FTIR spectra of the representative samples are shown in Figure 5. All of the spectra of TiO2, TCU4, TCU6 NCs, and bare CU (Figure S2) show the intense broad band for the M–O bond stretching frequency in the range of 400–800 cm–1.31 Low- and high-intensity bands are observed in the region of 400–700 cm–1 for tetrahedral and octahedral complexes in the spinel ferrite structure.29 It is also observed that, in the NCs, the M–O bond intensity increases as the concentration of TiO2 in the NCs increases. The band at 3000–3500 cm–1 is assigned to the stretching −OH vibrations of water.

Figure 5.

Figure 5

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FTIR spectra of (a) TiO2, (b) TCU4, and (c) TCU6 NCs.

UV–visible absorption spectra of the representative TCU NCs with bare materials are shown in Figure 6a,b. In the absorbance spectra of the composites with a larger content of TiO2, the strong optical absorption is observed in the range between 300 and 400 nm, while that with shifting of the absorption edge toward a longer wavelength is observed with the CU content in the bare TiO2. Moreover, the optical absorption also covered from 300 to 800 nm and further increased in absorption strength with the CU content in the composites compared to that of others. The wide coverage of optical absorption in the CU-dominant composites is due to its well-matchable visible–NIR-active optical absorption of CU compared to that of UV-active TiO2 contents.32 Among the composites, a more optical coverage of the electromagnetic spectrum and increase in the intensity of the absorption bands are observed for the TCU4 NCs compared to that of others, which would result in a strong optical absorption of electromagnetic radiation for efficient catalytic activity in the present reclamation reactions.

Figure 6.

Figure 6

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UV–visible DRS absorption spectra of (a) bare TiO2, TCU1 NCs, and TCU3 NCs, (c) bare CU, TCU4 NCs, and TCU6 NCs and optical band gaps of (b) bare TiO2, TCU1 NCs, and TCU3 NCs and (d) bare CU, TCU4 NCs, and TCU6 NCs.

The optical band gap of the samples is calculated by using a modified Tauc plot, which consists of (αhυ)1/2 versus photon energy (hυ). Tauc plots for the representative samples are shown in Figure 6c,d. Extrapolation of the absorbance edge to the x axis results in optical band gap values of 1.4 and 3.2 eV for bare CU and bare TiO2 NPs, respectively, which are in good agreement with those reported elsewhere.33 In addition, in the TiO2-dominant composites (from TCU1 to TCU3), the optical band gap value is near 3.2 eV, while other composites have optical band gap values in the range of 1.4–1.6 eV due to the mixing of HOMO–LUMO levels of the components.34 The optical band gap value of the samples is shown in the Supporting Information (Table S1). Based on these values, it is revealed that TCU4 NCs have a well-matchable optical absorbance (and hence Eg = 1.6 eV) with the solar spectrum as compared to the others.35 Therefore, the appropriate compositions of TiO2 and CU in the TCU composites (particularly TCU4) extends the more visible absorbance of the electromagnetic spectrum. In addition, the electron charge separation between the components also plays an important role in enhancing the catalytic activity of the composites. Due to the major content of CU in the TCU4 sample, after photoirradiation, the electrons from the valence band (VB) (−4.6 eV) of CU get excited to its CB (−3.4 eV), and then these electrons would transfer to the CB (−4.2 eV) of TiO2 due to their equivalent energy levels, while simultaneously, holes formed in the VB can be scavenged by the other moieties present in the waste in concordance with an earlier reported paper,36 and hence the electrons present in the CB encourage reduction of Ag(I) present in waste to Ag. Therefore, the representative TCU4 composites retard the electron–hole recombination rate more effectively, hence the better catalytic activity in the photochemical reactions for recovering the silver present in the waste.

N2 adsorption/desorption measurements of the representative TCU NCs are shown in Figure 7. The graph shows the existence of the characteristic type-IV isotherm with a mesoporous nature of the materials. The specific surface areas of TCU4 and TCU6 are found to be 50.46 and 34.18 m2/g–1, while the total pore volumes for these samples are 0.055 and 0.042 cc/g, respectively. The specific surface area and pore volume for the other composites are shown in the Supporting Information, Table S1. Among them, TCU4 NCs exhibit a higher surface area than that of other composites or bare materials. In the present investigation, the reported surface area parameters of the TCU4 NCs are controversial to that of the usual trends related to composite formations. This high specific surface area induces higher exposure to active sites, and this leads to higher catalytic activity for Ag(0) NP recovery from photographic effluent. However, the pore volume value of the composites is decreased significantly due to more interactions between the TiO2 and CU lattices revealing the close lattice formation, and hence these closer lattices would be preeminent in charge carrier separation in the photochemical processes.37

Figure 7.

Figure 7

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N2 adsorption–desorption isotherms of (a) TCU4 and (b) TCU6 NCs.

A magnetic hysteresis curve of the representative TCU4 NCs at room temperature is obtained by using VSM measurements with an applied field of −15,000 to 15,000 Oe, which is shown in Figure 8.

Figure 8.

Figure 8

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Hysteresis loop of TCU4 NCs.

The plot has an S-shaped curve without a hysteresis loop with a saturation magnetization (Ms) of 73.39 emu/g, hence confirming the superparamagnetic nature of TCU4 NCs. The observed saturation magnetization (Ms) value greater than 45.00 emu/g indicates the magnetically well separation properties of the desired catalyst, which facilitates the easy recovery of the catalysts from suspensions at room temperature.38

Standard Protocol for Photocatalytic Conversion of Ag(I) Ions to Ag(0) NPs

The photocatalytic conversion of Ag(I) ions into Ag(0) NPs is conducted by using the TCU NCs. During this photochemical conversions, the various reaction conditions such as the composition of the catalyst, initial concentration of Ag(I) ions, amount of the catalyst, and pH of the solution are optimized for efficient conversion to get Ag(0) NPs from the reaction mixture, which are also highlighted as follows.

Effect of Catalyst Composition

The photocatalytic reaction is carried out using the different TCU NCs. During each attempt, the reaction parameters such as the pH of the solution, amount of catalysts, concentration of Ag(I) ions, wavelength and intensity of visible irradiation, reaction time interval, etc. are kept constant except for the composition of the catalysts. The progress of the photochemical conversions is monitored through measuring the absorbance of the solution after 30 min using UV–visible measurements. Figure 9 shows the UV–visible absorbance spectra of the supernatant solution containing the recovered silver for the different NCs. The characteristic surface plasmon band at 417 nm of Ag(0) NPs for all the compositions of TCU NCs as well as bare CU except TiO2 NPs is seen. In bare TiO2, there is not any absorption band of the Ag(0) NPs revealing the negligible visible absorption made by the reaction mixture against its UV-active light irradiation, and in the case of bare CU, the lower intensity of the plasmon band reveals the recovery of Ag(0) NPs up to some extent due to absorption of visible–NIR radiation against visible incident photons. In connection to the NCs with a lower content of CU (from TCU1 to TCU3), the intensity of the surface plasmon band is lower revealing the little catalytic recovery of Ag(0) NPs, while the remaining NCs having more intense bands reveal somewhat a faster catalytic conversion rate for forming Ag(0) NPs. The lower rate of Ag(0) NP recovery for TCU1 to TCU3 is in consistency with the mismatch between their optical energy absorption and that of incident visible photons, while the somewhat higher rate of Ag(0) recovery from TCU6 to TCU4 is attributed to more absorption of visible–NIR radiation compared to that of incident visible photons. Among all the NCs, the higher rate of Ag(0) NP recovery is observed for TCU4 NCs due to the strong maximum optical absorbance with a well-matchable optical band gap in the visible region, greater specific surface area, and lower recombination rate of charge carriers.39

Figure 9.

Figure 9

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Effect of catalyst composition in TCU NCs on the photoconversion reaction of Ag(I) ions using various NCs after 120 min. {Experimental conditions: (1) [AgNO3] = 60 ppm, (2) volume of AgNO3 = 100 mL, (3) amount of catalyst = 300 mg, (4) pH of the solution = 9.00 ± 0.10, (5) wavelength 520 ± 40 nm, (6) intensity = 8 W, and (7) time interval = 120 min.}

Taking into consideration higher catalytic Ag(0) NP recovery, all further reclamation processes with variable reaction parameters are carried out using TCU4 NCs only.

Effect of pH Variation

The effect of pH is also an important parameter that could directly affect the aggregations the particles formed in the solution and hence the particle size of Ag(0) NPs formed. Figure 10 shows the absorbance of Ag(0) NPs formed with respect to the photon wavelength for the reaction mixtures having different pH values using TCU4 NCs under visible light irradiation. At pH = 9.00 ± 0.10, the strong surface plasmon band is appeared at 417 nm for smaller Ag(0) NPs due to the minimal effect of particle aggregations. This is attributed to the good capping of the particles formed in the nucleation stage by the surfactant as well as the availability of more functional moieties on the catalysts to interact with Ag(I) more strongly resulting in the uniform particles. However, in acidic conditions of the reaction mixture (pH = 3 ± 0.10), the absorbance of the analyte solution is observed at 803 nm of the larger Ag(0) NPs formed. Therefore, with a decrease in the pH of the reaction mixture, the absorbance band is shifted from 417 to 803 nm. Therefore, the aggregations of the particles, good capping of NPs by surfactants, availability of active sites on the catalysts for strong interactions, and hence size of the Ag(0) NPs formed are strongly dependent with the pH of the reaction mixture. These results are also in good consistency with the research endeavors related to behaviors of Ag NPs in wastewater.40 With this present investigation, the catalytic recovery of Ag(0) NPs from the waste is conducted at pH = 9.00 of the solution.

Figure 10.

Figure 10

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Effect of the pH of Ag(I) ion on the photoconversion reaction of Ag(I) into Ag(0) NPs in the presence of TCU4 NCs under visible irradiation. {Experimental conditions: (1) [AgNO3] = 60 ppm, (2) volume of AgNO3 = 100 mL, (3) amount of the catalyst = 300 mg, (4) catalyst = TCU4, (5) wavelength = 520 ± 40 nm, (6) intensity = 8 W, and (7) time interval = 120 min.}

Effect of the Initial Concentration of the Ag(I) Solution

Figure 11 shows the absorbance of Ag(0) NPs formed with respect to the photon wavelength for the reaction mixtures having different concentrations of Ag(I) ions (from 20 to 80 ppm) using TCU4 NCs under visible light irradiation. From the figure, it is seen that, as the concentration of Ag(I) ions increases from 20 to 60 ppm, the surface plasmon band absorbance at 417 nm of Ag(0) NPs formed increases, while thereafter it decreases beyond a 60 ppm concentration of Ag(I) ions. For a higher concentration of Ag(I) ions, a greater number of highly energetic particles having smaller diameters would be formed in the nucleation stage, and then these energetic particles undergo Ostwald ripening at a very high rate resulting in somewhat bigger particles in the reaction mixture. Therefore, at 80 ppm concentrations of Ag(I) ions, the overall number of Ag(0) NPs is less, which is reflected through the decrease in the intensity of the characteristic surface plasmon band of the Ag(0) NPs.41 Based on this investigation, a greater number of Ag(0) NPs are formed at 60 ppm concentrations of Ag(I) ions, and hence this concentration of Ag(I) ions is fixed during the catalytic recovery of Ag(0) NPs from photographic waste.

Figure 11.

Figure 11

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Effect of the initial concentration of Ag(I) ions on the photoconversion reaction of Ag(I) into Ag(0) NPs in the presence of TCU4 NCs under visible irradiation. {Experimental conditions: (1) pH of AgNO3 = 9.00 ± 0.10, (2) volume of AgNO3 = 100 mL, (3) amount of catalyst = 300 mg, (4) catalyst = TCU4, (5) wavelength 520 ± 40 nm, (6) intensity = 8 W, and (7) time interval = 120 min.}

Effect of the Amount of the Catalyst

To analyze the effect of the amount of the catalyst on the photoconversion reaction of Ag(I) ions into the Ag(0) NPs, the amount of the TCU4 catalyst is varied from 100 to 500 mg keeping other experimental conditions constant. Figure 12 shows the absorbance of Ag(0) NPs formed with respect to the photon wavelength for the reaction mixtures containing different amounts of the TCU4 catalyst. It is seen that, as the amount of the catalyst increases from 100 to 300 mg, the absorbance strength of the characteristic absorbance maxima also increases. However, beyond 300 mg, the excess addition of the catalyst decreases the absorbance strength of recovered Ag(0) NPs. These observations of decreasing absorbance intensity of the characteristic band are also reflected through an increase in turbidity of the reaction mixture during photochemical conversions.42 This increase in the turbidity of the solution for higher amounts of TCU4 (600 mg) retards the intensity of incident photons reaching the interactions of Ag(I) ions with the catalysts, and hence a lower number of Ag(0) NPs are formed as derived from the intensity of the plasmon band.

Figure 12.

Figure 12

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Effect of the catalyst amount on the photoconversion reaction of Ag(I) into Ag(0) NPs in the presence of TCU4 NCs under visible irradiation. {Experimental conditions: (1) pH of AgNO3 = 9.00 ± 0.10, (2) volume of AgNO3 = 100 mL, (3) [AgNO3] = 60 ppm, (4) catalyst = TCU4, (5) wavelength 520 ± 40 nm, (6) intensity = 8 W, and (7) time interval = 120 min.}

All these optimized experimental parameters of the photoconversion reaction of the Ag(I) ion into the Ag(0) NPs are applied for the recovery of Ag(0) NPs from the photographic waste.

Application to Photographic Effluent Solutions

After proper sampling of photoprocessing waste, it is treated to recover Ag(0) NPs using the optimized parameters of a model reaction with TCU4 NCs in visible light irradiation, and the progress of the reaction is monitored through UV–visible measurements. Figure 13 shows the UV–visible pattern of the Ag(0) NPs recovered from photographic waste at pH = 9.00. The surface palsmon band at 421 nm is observed revealing the formation of Ag(0) NPs from the photoprocessing waste. The similar treatment is also applied to photoprocessing waste at pH = 3.00 by keeping the optimized parameters constant, and hence the formation of larger Ag(0) NPs is confirmed through the UV–visible band (inset of UV–visible spectrum, Figure 13) shifted at 802 nm.40 In addition, the concentration of Ag(0) NPs recovered from photoprocessing waste is determined by using the following equation:43

Figure 13.

Figure 13

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Photoconversion reaction of photographic waste to Ag(0) NPs using TCU4 NCs. {Experimental conditions: (1) amount = 300 mg, (2) volume of photographic waste = 100 mL, (3) [photographic waste] = 60 ppm, (4) catalyst = TCU4, (5) wavelength = 520 ± 40 nm, (6) intensity = 8 W, and (7) time interval = 120 min.}

C = NT/NVNAwhere C is the molar concentration of the nanoparticle solution, NT is the total number of silver atoms added, N is the Ag(0) NPs’ number of atoms per NP, V is the Ag(0) NPs’ volume of the reaction solution in liters, and NA is the Avogadro’s number of Ag(0) NPs (6.023 × 1023). In the present investigation, the catalytic conversion efficiencies of 89.50% and 98.00% are obtained for Ag(0) NPs recovered from photoprocessing waste at pH 3 and 9, respectively.

The formation of smaller or larger Ag(0) NPs at the different pH values is also confirmed through HRTEM images, and these images are shown in Figure 14a,b. The Ag(0) NPs recovered at the different pH values are spherical in shape. The average diameter of Ag(0) NPs recovered at pH = 9.00 is observed to be approximately 15 nm, while the average diameter of Ag(0) NPs recovered at pH = 3.00 is approximately 72 nm. These observations are also in good agreement with the results observed in the optimized model reaction at the different pH values. Therefore, smaller Ag(0) NPs are formed for the acidic pH compared to those of the basic pH of the reaction mixture under the optimized experimental conditions, and hence these smaller particles having higher surface areas would have better catalytic activity in the antibacterial studies. HRTEM images also show that the lattice crystal fringe value of 0.232 nm corresponds to a characteristic (111) plane of Ag(0) NPs formed.

Figure 14.

Figure 14

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HRTEM images of recovered nanocrystalline silver formation for (a) pH = 9 and (c) pH = 3 and lattice fringes of (b) pH = 9 and (d) pH = 3.

The spherically shaped Ag(0) NPs show higher antibacterial activity against bacteria due to higher surface areas for better contact with microorganisms, so the spherically shaped Ag(0) NPs were used for photoinactivation of bacteria in a test against E. coli bacteria.44

Antimicrobial Activity of Recovered Ag(0) NPs

Due to the smaller Ag(0) NPs recovered from waste at pH = 9.00, these NPs are further used to test antibacterial activity against E. coli bacteria. In this study, the antibacterial activity of Ag(0) NPs against E. coli is carried using the varying concentrations of Ag(0) NPs recovered from 25 μL up to 100 μL, and hence complete killing of E. coli bacteria is observed in 120 min using Ag(0) NPs. The antibacterial results obtained using an agar disc diffusion method are shown in Figure 15.

Figure 15.

Figure 15

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Antibacterial activity of recovered Ag(0) NPs by the agar disc diffusion method.

Agar Disc Diffusion Method

Figure 15 shows the zone of inhibition (ZOI) of E. coli control using recovered Ag(0) NPs. It is seen that the diameter of ZOI is increased with an increase in the concentration of Ag(0) NPs up to 100 μL. The highest diameter (3.2 cm) of the ZOI for E. coli control is observed for 100 μL concentrations of Ag(0) NPs, while 2.3 cm and 1.4 cm diameters are observed for 50 and 25 μL concentrations of Ag(0) NPs, respectively. Therefore, the recovered Ag(0) NPs are good antibacterial agents against E. coli, and hence these results are in good agreement with others.45,46

Conclusions

The easy and sustainable protocol has been successful used to recover Ag(0) NPs from photographic waste using magnetically separable TiO2@CuFe2O4 NCs, and thereafter the recovered NPs are tested against the E. coli bacteria for antibacterial studies. The different compositions of TiO2@CuFe2O4 NCs are synthesized using the wet-chemical ex situ method at 110 °C. The prominent tetragonal-phase dominance of the respective components is confirmed through XRD measurements. A wide visible optical coverage for the NCs is observed compared to that of UV-active TiO2 NPs or visible–NIR CU NPs. Magnetic VCM measurements reveal the superparamagnetic nature of TCU4 NCs with a saturation magnetization (Ms) value of 73.39 emu/g, which confirms the magnetically separable nature of TCU4 NCs. The standard protocol for conversion of Ag(I) ions to Ag(0) NPs is established with the various optimized parameters under visible photoirradiation. Then, the optimized protocol is adopted for the recovery of Ag(0) NPs from photographic waste solutions, and hence, further, these recovered Ag(0) NPs from photographic waste are used as efficient antibacterial agents against E. coli.

Experimental Section

Materials

All the chemicals were purchased from Sigma-Aldrich, and these are used directly without purification for recovery of colloidal Ag(0) NPs.

Synthesis of Bare Materials and Their Nanocomposites

Synthesis of Nanocrystalline CuFe2O4 (CU)

Nanocrystalline CU is prepared by using a sol–gel autocombustion method. First, the stoichiometric amount of metal nitrates is dissolved in a minimum quantity of deionized water and mixed together. This resulting solution is subjected to the addition of citric acid as fuel for the combustion process as well as CTAB as a capping agent under constant stirring. The pH of the resulting solution is adjusted to 9.00 ± 0.10 using ammonia. During the addition of ammonia, the color of the solution is varied from green to black. Then, the mixture is heated to 250 °C until combustion occurs. After combustion, the powder is cooled at room temperature and sintered at 500 °C for 6 h.

Synthesis of TiO2 NPs

TiO2 NPs are prepared by a sol–gel route. Synthesis of TiO2 is carried out by an earlier reported paper to get anatase-phase TiO2.47

Synthesis of TiO2@CuFe2O4 (TCU) NCs

The synthesis of TCU NCs is carried out by an ex situ method. As per respective compositions, the desired weight percent of TiO2 as well as CU is dispersed in 10 mL ethanol in a beaker, and then the overall content is stirred for 4 h. Subsequently, the solution is ultrasonicated for 60 min to ensure proper dispersion. After that, the precipitate is separated and dried in an electric oven at 110 °C. In a similar way, the different compositions such as TCU1 (TiO2 = 99.0%, CU = 1.0%), TCU2 (TiO2 = 95.0%, CU = 5.0%), TCU3 (TiO2 = 90.0%, CU = 10.0%), TCU4 (TiO2 = 10.0%, CU = 90.0%), TCU5 (TiO2 = 5.0%, CU = 95.0%), and TCU6 (TiO2 = 1.0%, CU = 99.0%) NCs are synthesized with the respective amount of TiO2 as well as CU.

Catalytic Reclamation of Silver from Photographic Waste

The catalytic reclamation of silver present in the photographic waste is carried out using the different steps, namely, development of a standard protocol, optimization of the various preparative parameters such as the pH of the solution, composition of the catalysts, amount of the catalysts, etc., and thereafter the optimized standard protocol is used for treating the photochemical waste to recover silver in the nanoscale dimensions.

Designing of the Standard Protocol for Forming Nanocrystalline Silver from Ag(I) Ions

In the standard protocol, the Ag(I) ions are reduced to colloidal Ag(0) NPs using NCs under visible light irradiation (wavelength of 520 ± 40 nm with an intensity of 8 W) at room temperature. During this conversion, the various reaction conditions such as the composition of the catalyst, initial concentration of AgNO3, amount of the catalyst, and pH of the reaction mixture are optimized for efficient conversion. An amount of desired TCU NCs as the photocatalyst is dispersed in varying concentrations of AgNO3 (20 ppm, 100 mL) and sodium lauryl sulfate aqueous solution (0.30 g). After a fixed irradiation time interval (30 min), 2.0 mL aliquots are collected, and then the catalyst from an aliquot is separated magnetically. Then, the absorbance of the supernatant solution is measured with the help of a UV–visible spectrophotometer.

Treatment of Photographic Waste for Reclaiming Ag(0) NPs

Initially, the photographic waste is aerated to oxidize the moieties present in it as well as to remove the dissolved gases. Then, it is treated with sodium thiosulfate solution, and thereafter it is centrifuged to remove the suspended or solid particles. Then, the supernatant solution is further treated with NCs as per optimized condition used in the standard protocol. The progress of catalytic reclamation is monitored by UV–visible spectrophotometer measurements. Also, the morphology with the size of recovered silver particles is confirmed through HRTEM with SAED patterns.

Antibacterial Activity of Recovered Ag(0) NPs

The recovered nanocrystalline silver is further used against the photocatalytic antibacterial studies. The antimicrobial activity of recovered Ag(0) NPs has been studied against gram-negative E. coli. All labware are sterilized by autoclaving at 120 °C for 30 min. The testing microorganism E. coli is cultured on nutrient agar plates at 37 °C for 24 h, and the inhibitory effects of Ag(0) NPs on microorganisms are tested by using the agar disc diffusion method.

Agar Disc Diffusion Method

A bacterial suspension is prepared in a 10 mL saline solution to obtain a final concentration up to 108 CFU mL–1. This bacterial suspension is spread on previously prepared agar petriplates.48 Sterilized Whatmann paper was cut in disc shapes with a 5 mm diameter and soaked into the colloidal Ag(0) NP solution with different volumes (25, 50, and 100 μL). Due to this, adsorption of Ag(0) NPs on the disc takes place, and the appropriate results could be obtained. Microbial strains are then allowed to grow for 24 h at 37 °C.49 The inhibitory effect on microorganisms is evaluated by calculating the diameter of the zone of inhibition (ZOI) surrounding the paper disc.

Measurements

Thermal stability of the ferrite sample was measured by a thermogravimetric instrument (SDT Q600 V20.9 Build 20). X-ray diffraction (XRD) analysis of the samples was done in the 2θ range from 10–80° on an X-ray diffractometer (Bruker, D8 Advance) with Cu Kα radiation. The surface morphology of nanomaterials was studied using field emission scanning electron microscopy (FESEM) (FEI, Nova NanoSEM 450), and elemental analysis was obtained on a scanning electron microscope with an energy-dispersive atomic X-ray (EDAX) spectrometer(JEOL JSM 6360 LV). The particle size of the representative NCs was confirmed using high-resolution transmission electron microscopy (FEI, Tecnai F20). Diffuse reflectance (DR) spectra of the samples were recorded using a UV–vis spectrophotometer (LabIndia, UV 3092). The vibrating sample magnetometer (VSM) analysis of NCs is recorded on Lakeshore VSM 7410 to get the hysteresis loop. The detailed characterization of TiO2 is reported in our earlier paper.47

Acknowledgments

V.B.S. thanks the University Grants Commission, New Delhi, India, for financial support under the basic science research program.

Supporting Information Available

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsomega.9b03260.

  • Photoconversion reaction of photographic waste to Ag(0) NPs using TCU4 NCs and table of the optical energy band gap of the desired materials (PDF)

Author Contributions

The final version of the manuscript is approved by all complainants.

The authors declare no competing financial interest.

Supplementary Material

ao9b03260_si_001.pdf (190.9KB, pdf)

References

  1. Jeyaseelan S.; Sathananthan S. Clean technology for treatment of photographic wastes and silver recovery. Environ. Monit. Assess. 1997, 44, 219–229. 10.1023/A:1005784523501. [DOI] [Google Scholar]
  2. Saman N.; Johari K.; Song S. T.; Mat H. Silver adsorption enhancement from aqueous and photographic waste solutions by mercerized coconut fiber. Sep. Sci. Technol. 2015, 50, 937–946. 10.1080/01496395.2015.1004346. [DOI] [Google Scholar]
  3. El-Rafie M. H.; Mohamed A. A.; Shaheen T. I.; Hebeish A. Antimicrobial effect of silver nanoparticles produced by fungal process on cotton fabrics. Carbohydr. Polym. 2010, 80, 779–782. 10.1016/j.carbpol.2009.12.028. [DOI] [Google Scholar]
  4. Martínez-Gutierrez F.; Thi E. P.; Silverman J. M.; de Oliveira C. C.; Svensson S. L.; Hoek A. V.; Sánchez E. M.; Reiner N. E.; Gaynor E. C.; Pryzdial E. L. G.; Conway E. M.; Orrantia E.; Ruiz F.; Av-Gay Y.; Bach H. Antibacterial activity, inflammatory response, coagulation and cytotoxicity effects of silver nanoparticles. Nanomed.: Nanotechnol., Biol. Med. 2012, 8, 328–336. 10.1016/j.nano.2011.06.014. [DOI] [PubMed] [Google Scholar]
  5. AshaRani P. V.; Low Kah Mun G.; Hande M. P.; Valiyaveettil S. Cytotoxicity and genotoxicity of silver nanoparticles in human cells. ACS Nano 2009, 3, 279–290. 10.1021/nn800596w. [DOI] [PubMed] [Google Scholar]
  6. Aliotta J., Silver Recovery and Refining from Photographic Solutions. In Precious Metals 1982; Elsevier: 1983, pp 597–601. [Google Scholar]
  7. Nawaz T.; Sengupta S. Silver recovery from laundry washwater: the role of detergent chemistry. ACS Sustainable Chem. Eng. 2017, 6, 600–608. 10.1021/acssuschemeng.7b02933. [DOI] [Google Scholar]
  8. Hosseini S. G.; Pourmortazavi S. M.; Fathollahi M. Orthogonal array design for the optimization of silver recovery from waste photographic paper. Sep. Sci. Technol. 2005, 39, 1953–1966. 10.1081/SS-120035939. [DOI] [Google Scholar]
  9. Choi C.; Cui Y. Recovery of silver from wastewater coupled with power generation using a microbial fuel cell. Bioresour. Technol. 2012, 107, 522–525. 10.1016/j.biortech.2011.12.058. [DOI] [PubMed] [Google Scholar]
  10. Songkroah C.; Nakbanpote W.; Thiravetyan P. Recovery of silver-thiosulphate complexes with chitin. Process Biochem. 2004, 39, 1553–1559. 10.1016/S0032-9592(03)00284-X. [DOI] [Google Scholar]
  11. a Mulfinger L.; Solomon S. D.; Bahadory M.; Jeyarajasingam A. V.; Rutkowsky S. A.; Boritz C. Synthesis and study of silver nanoparticles. J. Chem. Educ. 2007, 84, 322. 10.1021/ed084p322. [DOI] [Google Scholar]
  12. Prathna T. C.; Chandrasekaran N.; Raichur A. M.; Mukherjee A. Biomimetic synthesis of silver nanoparticles by Citrus limon (lemon) aqueous extract and theoretical prediction of particle size. Colloids Surf., B 2011, 82, 152–159. 10.1016/j.colsurfb.2010.08.036. [DOI] [PubMed] [Google Scholar]
  13. Jana N. R.; Gearheart L.; Murphy C. J. Wet chemical synthesis of silver nanorods and nanowires of controllable aspect ratioElectronic supplementary information (ESI) available: UV–VIS spectra of silver nanorods. Chem. Commun. 2001, 7, 617–618. 10.1039/B100521I. [DOI] [Google Scholar]
  14. Wei W.; Li A.; Pi S.; Wang Q.; Zhou L.; Yang J.; Ma F.; Ni B.-J. Synthesis of Core–Shell Magnetic Nanocomposite Fe3O4@ Microbial Extracellular Polymeric Substances for Simultaneous Redox Sorption and Recovery of Silver Ions as Silver Nanoparticles. ACS Sustainable Chem. Eng. 2018, 749. 10.1021/acssuschemeng.7b03075. [DOI] [Google Scholar]
  15. Selvakannan P.; Swami A.; Srisathiyanarayanan D.; Shirude P. S.; Pasricha R.; Mandale A. B.; Sastry M. Synthesis of aqueous Au core– Ag shell nanoparticles using tyrosine as a pH-dependent reducing agent and assembling phase-transferred silver nanoparticles at the air– water interface. Langmuir 2004, 20, 7825–7836. 10.1021/la049258j. [DOI] [PubMed] [Google Scholar]
  16. Jiang B.; Wu Q.; Zhang L.; Zhang Y. Preparation and application of silver nanoparticle-functionalized magnetic graphene oxide nanocomposites. Nanoscale 2017, 9, 1607–1615. 10.1039/C6NR09260H. [DOI] [PubMed] [Google Scholar]
  17. Yin X.; Long J.; Xi Y.; Luo X. Recovery of Silver from Wastewater Using a New Magnetic Photocatalytic Ion-Imprinted Polymer. ACS Sustainable Chem. Eng. 2017, 5, 2090–2097. 10.1021/acssuschemeng.6b01871. [DOI] [Google Scholar]
  18. Li X. G.; Feng H.; Huang M. R. Redox Sorption and Recovery of Silver Ions as Silver Nanocrystals on Poly (aniline-co-5-sulfo-2-anisidine) Nanosorbents. Chem. - A Eur. J. 2010, 16, 10113–10123. 10.1002/chem.201000506. [DOI] [PubMed] [Google Scholar]
  19. Li H.; Bian Z.; Zhu J.; Huo Y.; Li H.; Lu Y. Mesoporous Au/TiO2 nanocomposites with enhanced photocatalytic activity. J. Am. Chem. Soc. 2007, 129, 4538–4539. 10.1021/ja069113u. [DOI] [PubMed] [Google Scholar]
  20. Huang Z.; Zhu Y.; Wang S.; Yin G. Controlled growth of aligned arrays of Cu– Ferrite nanorods. Cryst. Growth Des. 2006, 6, 1931–1935. 10.1021/cg0505517. [DOI] [Google Scholar]
  21. Chandrasekaran S.; Bowen C.; Zhang P.; Li Z.; Yuan Q.; Ren X.; Deng L. Spinel photocatalysts for environmental remediation, hydrogengeneration, CO2 reduction and photoelectrochemical water splitting. J. Mater. Chem. A 2018, 6, 11078. 10.1039/C8TA03669A. [DOI] [Google Scholar]
  22. Karunakaran C.; Vinayagamoorthy P.; Jayabharathi J. Enhanced photocatalytic activity of magnetically separable bactericidal CuFe2O4-embedded Ag-deposited ZnO nanosheets. RSC Adv. 2016, 6, 1782–1791. 10.1039/C5RA20958G. [DOI] [Google Scholar]
  23. Schneider J.; Matsuoka M.; Takeuchi M.; Zhang J.; Horiuchi Y.; Anpo M.; Bahnemann D. W. Understanding TiO2 Photocatalysis: Mechanisms and Materials. Chem. Rev. 2014, 114, 9919–9986. 10.1021/cr5001892. [DOI] [PubMed] [Google Scholar]
  24. Nada A. A.; Nasr M.; Viter R.; Miele P.; Roualdes S.; Bechelany M. Mesoporous ZnFe2O4@TiO2 Nanofibers Prepared by Electrospinning Coupled to PECVD as Highly Performing Photocatalytic Materials. J. Phys. Chem. C 2017, 121, 24669–24677. 10.1021/acs.jpcc.7b08567. [DOI] [Google Scholar]
  25. Wang M.; Sun L.; Cai J.; Huang P.; Su Y.; Lin C. A facile hydrothermal deposition of ZnFe2O4 nanoparticles on TiO2 nanotube arrays for enhanced visible light photocatalytic activity. J. Mater. Chem. A 2013, 1, 12082. 10.1039/c3ta12577g. [DOI] [Google Scholar]
  26. Lei B.-X.; Sun W.; Sun Z.-F. Synthesis of visible-light absorbing CoFe2O4 sensitized TiO2 nanotube arrays electrode with enhanced photoelectrochemical performance. Mater. Res. Bull. 2013, 48, 3625–3629. 10.1016/j.materresbull.2013.04.085. [DOI] [Google Scholar]
  27. Kim H. S.; Kim D.; Kwak B. S.; Han G. B.; Um M.-H.; Kang M. Synthesis of magnetically separable core@shell structured NiFe2O4@TiO2 nanomaterial and its use for photocatalytic hydrogen production by methanol/water splitting. Chem. Eng. J. 2014, 243, 272–279. 10.1016/j.cej.2013.12.046. [DOI] [Google Scholar]
  28. Stamplecoskie K. G.; Scaiano J. C. Light emitting diode irradiation can control the morphology and optical properties of silver nanoparticles. J. Am. Chem. Soc. 2010, 132, 1825–1827. 10.1021/ja910010b. [DOI] [PubMed] [Google Scholar]
  29. Altincekic T. G.; Boz İ.; Baykal A.; Kazan S.; Topkaya R.; Toprak M. S. Synthesis and characterization of CuFe2O4 nanorods synthesized by polyol route. J. Alloys Compd. 2010, 493, 493–498. 10.1016/j.jallcom.2009.12.140. [DOI] [Google Scholar]
  30. Selvan R. K.; Krishnan V.; Augustin C. O.; Bertagnolli H.; Kim C. S.; Gedanken A. Investigations on the structural, morphological, electrical, and magnetic properties of CuFe2O4– NiO nanocomposites. Chem. Mater. 2008, 20, 429–439. 10.1021/cm701937q. [DOI] [Google Scholar]
  31. Jhuang Y.-Y.; Cheng W.-T. Fabrication and characterization of silver/titanium dioxide composite nanoparticles in ethylene glycol with alkaline solution through sonochemical process. Ultrason. Sonochem. 2016, 28, 327–333. 10.1016/j.ultsonch.2015.08.011. [DOI] [PubMed] [Google Scholar]
  32. Roy N.; Sohn Y.; Pradhan D. Synergy of low-energy {101} and high-energy {001} TiO2 crystal facets for enhanced photocatalysis. ACS Nano 2013, 7, 2532–2540. 10.1021/nn305877v. [DOI] [PubMed] [Google Scholar]
  33. Delekar S. D.; Dhodamani A. G.; More K. V.; Dongale T. D.; Kamat R. K.; Acquah S. F. A.; Dalal N. S.; Panda D. K. Structural and Optical Properties of Nanocrystalline TiO2 with Multiwalled Carbon Nanotubes and Its Photovoltaic Studies Using Ru(II) Sensitizers. ACS Omega 2018, 3, 2743–2756. 10.1021/acsomega.7b01316. [DOI] [PMC free article] [PubMed] [Google Scholar]
  34. Golshan M.; Kakavandi B.; Ahmadi M.; Azizi M. Photocatalytic activation of peroxymonosulfate by TiO2 anchored on cupper ferrite (TiO2@CuFe2O4 ) into 2,4-D degradation: Process feasibility, mechanism and pathway. J. Hazard. Mater. 2018, 359, 325–337. 10.1016/j.jhazmat.2018.06.069. [DOI] [PubMed] [Google Scholar]
  35. Deshmukh S. P.; Mullani S. B.; Koli V. B.; Patil S. M.; Kasabe P. J.; Dandge P. B.; Pawar S. A.; Delekar S. D. Ag Nanoparticles Connected to the Surface of TiO2 Electrostatically for Antibacterial Photoinactivation Studies. Photochem. Photobiol. 2018, 1249. 10.1111/php.12983. [DOI] [PubMed] [Google Scholar]
  36. Huang M.; Tso E.; Datye A. K.; Prairie M. R.; Stange B. M. Removal of Silver in Photographic Processing Waste by TiO2-Based Photocatalysis. Environ. Sci. Technol. 1996, 30, 3084–3088. 10.1021/es960167l. [DOI] [Google Scholar]
  37. Patil S. M.; Dhodamani A. G.; Vanalakar S. A.; Deshmukh S. P.; Delekar S. D. Multi-applicative tetragonal TiO2 /SnO2 nanocomposites for photocatalysis and gas sensing. J. Phys. Chem. Solids 2018, 115, 127–136. 10.1016/j.jpcs.2017.12.020. [DOI] [Google Scholar]
  38. Nguyen A. T.; Nguyen L. T. M.; Nguyen C. K.; Truong T.; Phan N. T. S. Superparamagnetic Copper Ferrite Nanoparticles as an Efficient Heterogeneous Catalyst for the α-Arylation of 1, 3-Diketones with C—C Cleavage. ChemCatChem 2014, 6, 815–823. 10.1002/cctc.201300708. [DOI] [Google Scholar]
  39. Fu Y.; Chen Q.; He M.; Wan Y.; Sun X.; Xia H.; Wang X. Copper ferrite-graphene hybrid: a multifunctional heteroarchitecture for photocatalysis and energy storage. Ind. Eng. Chem. Res. 2012, 51, 11700–11709. 10.1021/ie301347j. [DOI] [Google Scholar]
  40. Andreescu D.; Eastman C.; Balantrapu K.; Goia D. V. A simple route for manufacturing highly dispersed silver nanoparticles. J. Mater. Res. 2007, 22, 2488–2496. 10.1557/jmr.2007.0308. [DOI] [Google Scholar]
  41. Sobczak-Kupiec A.; Malina D.; Wzorek Z.; Zimowska M. Influence of silver nitrate concentration on the properties of silver nanoparticles. Micro Nano Lett. 2011, 6, 656. 10.1049/mnl.2011.0152. [DOI] [Google Scholar]
  42. Gupta V. K.; Jain R.; Mittal A.; Mathur M.; Sikarwar S. Photochemical degradation of the hazardous dye Safranin-T using TiO2 catalyst. J. Colloid Interface Sci. 2007, 309, 464–469. 10.1016/j.jcis.2006.12.010. [DOI] [PubMed] [Google Scholar]
  43. Kalishwaralal K.; BarathManiKanth S.; Pandian S. R. K.; Deepak V.; Gurunathan S. Silver nanoparticles impede the biofilm formation by Pseudomonas aeruginosa and Staphylococcus epidermidis. Colloids Surf., B 2010, 79, 340–344. 10.1016/j.colsurfb.2010.04.014. [DOI] [PubMed] [Google Scholar]
  44. Rai M.; Yadav A.; Gade A. Silver nanoparticles as a new generation of antimicrobials. Biotechnol. Adv. 2009, 27, 76–83. 10.1016/j.biotechadv.2008.09.002. [DOI] [PubMed] [Google Scholar]
  45. Paredes D.; Ortiz C.; Torres R. Synthesis, characterization, and evaluation of antibacterial effect of Ag nanoparticles against Escherichia coli O157: H7 and methicillin-resistant Staphylococcus aureus (MRSA). Int. J. Nanomed. 2014, 9, 1717. 10.2147/IJN.S57156. [DOI] [PMC free article] [PubMed] [Google Scholar]
  46. Guzman M.; Dille J.; Godet S. Synthesis and antibacterial activity of silver nanoparticles against gram-positive and gram-negative bacteria. Nanomed.: Nanotechnol., Biol. Med. 2012, 8, 37–45. 10.1016/j.nano.2011.05.007. [DOI] [PubMed] [Google Scholar]
  47. Shevale V. B.; Dhodamani A. G.; Koli V. B.; Barkul R. P.; Jadhav J. P.; Delekar S. D. Efficient degradation of Azorubin S colourant in the commercial jam-jelly food samples using TiO2-CoFe2O4 nanocomposites in visible light. Mater. Res. Bull. 2017, 89, 79–88. 10.1016/j.materresbull.2017.01.012. [DOI] [Google Scholar]
  48. Krishnadevi K.; Selvaraj V.; Prasanna D. Thermal, mechanical and antibacterial properties of cyclophosphazene incorporated benzoxazine blended bismaleimide composites. RSC Adv. 2015, 5, 913–921. 10.1039/C4RA10564H. [DOI] [Google Scholar]
  49. Valgas C.; Souza S. M. D.; Smânia E. F. A.; Smânia A. Jr. Screening methods to determine antibacterial activity of natural products. Braz. J. Microbiol. 2007, 38, 369–380. 10.1590/S1517-83822007000200034. [DOI] [Google Scholar]

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Supplementary Materials

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