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. 2020 Jun 29;5(27):16670–16680. doi: 10.1021/acsomega.0c01555

Precursor- and Time-Dependent Morphological Evolution of ZnO Nanostructures for Comparative Photocatalytic Activity and Adsorption Dynamics with Methylene Blue Dye

Smriti Thakur 1, Sanjay K Mandal 1,*
PMCID: PMC7364575  PMID: 32685834

Abstract

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Diverse ZnO nanostructures were successfully fabricated at 700 °C by direct annealing of 1D Zn(II) coordination polymer precursors, namely, [Zn2(bpma)2(adc)2]n, [Zn2(bpea)2(adc)2]n, and {[Zn2(bpta)2(adc)2]·2H2O}n. The effect of sacrificial ligands present in the precursors as well as a variation in the retention time (6–24 h) during their synthesis resulted in 0D nanospheres, 1D microrods, and 3D polyhedra (with a diamond-like structure) of ZnO. The as-synthesized ZnO nanostructures were characterized by field-emission scanning electron microscopy, transmission electron microscopy, X-ray diffractometry, diffuse reflectance spectroscopy, and Raman spectroscopy. The hexagonal crystal structure was confirmed for all the ZnO samples. A lattice spacing of 0.22 nm has been observed for nanospheres, whereas a lattice spacing of 0.26 nm has been observed for the polyhedra. Their Raman spectra confirm the wurtzite phase of ZnO. UV–vis spectra of ZnO nanostructures exhibit broad peaks in the range of 350–370 nm, and the band gap energies are found to be in the range of 3.02–3.20 eV. Based on the photoluminescence spectra photocatalytic activities of the as-synthesized ZnO nanostructures calcined for 12 h were tested with methylene blue (MB) as a contaminant in an aqueous solution. These results demonstrate that the photocatalytic efficiency of polyhedra is higher than those of nanospheres and microrods. The adsorption kinetics of MB dye by these nanostructures were studied by three different kinetic models—Elovich’s, intraparticle, and pseudo-second-order. The maximum rate of adsorption was observed with the intraparticle diffusion model.

Introduction

Nanostructured semiconductor oxides have drawn a great deal of attention owing to their interesting optical and electrical properties, which makes their potential use in the field of optoelectronics, sensing, photovoltaics, and catalysis.1−5 However, designing and fabricating nanostructured oxides for their potential use in photocatalysis has always been an area of interest. There are several semiconductor oxides such as ZnO, SnO2, TiO2, and ZrO2, which are found to be efficient photocatalysts.6−9 These oxides can successfully oxidize the organic dye pollutants in waste water. Among these oxides, ZnO has been widely used as the most effective heterogeneous catalyst in photochemical reactions for solving the problems of waste water purification and combating the environmental pollution by degrading the harmful organic pollutants and dyes.10−13 This is due to its wide direct energy band gap of 3.3 eV and a large excitonic binding energy of 60 meV14 that are also responsible for other applications in solar cells, optics, LEDs, UV detectors, UV emitting devices, and biosensors.15−27 Thus, special emphasis has been given for the synthesis of ZnO to have a control over the size, shape, and composition. The need to develop the strategy for constructing ZnO nanostructures and understanding the underlying growth mechanism is highly desired.

Various synthetic routes like hydrothermal synthesis, sonochemical synthesis, thermal decomposition, chemical precipitation, ball milling, microemulsion synthesis, sol gel process, vapor phase synthesis, and the pulsed laser ablation technique28−39 have been applied for the preparation of ZnO nanomaterials. Nowadays, the solid-phase fabrication of metal oxides with unique sizes and morphologies via calcination of coordination polymers (CPs) under various conditions has become a suitable and convenient approach.40−42 In this approach, the CPs serve not only as starting materials but also act as stabilizers of the formed nanomaterials. The simple calcination method provides a new paradigm in the synthesis of tailor-made metal oxide nanomaterials. The desired properties of nanomaterials (e.g., luminescence,43 ferromagnetism,44 and cytotoxicity45) are dependent not only on the size but also on the appropriate morphology.46,47 Therefore, development of new efficient and cheap methods for the synthesis of nanomaterials with a desired size and morphology is very much required. In this regard, CPs serve as an important bridge between the synthetic chemistry and the materials science. This methodology has been used in the fabrication of various metal oxides, for example, PbO, ZnO, Fe2O3, Co3O4, CuO/Cu2O, and Tl2O3.48−54 Although the use of CPs as precursors for the synthesis of ZnO has not been established thoroughly, few groups have reported the preparation of these oxides. For example, (a) Oh’s group55 synthesized the ZnO rings and hexagonal tubes by calcination of a CP consisting of hexagonal lumps, (b) Zhang and co-workers56 reported the synthesis of superhydrophobic ZnO utilizing a superhydrophobic Zn(II) CP, and (c) Morsali’s group57 also synthesized ZnO nanoparticles from a Zn(II) nitrite CP in oleic acid. The metal ions with a standard reduction potential of 0.27 V or higher such as Co, Ni, and Cu present in CPs form pure metal nanoparticles during calcination, whereas metal ions with a reduction potential lower than 0.27 V such as Mg, Al, Mn, Zn, or Cr present in CPs tend to form corresponding metal oxides.58 Thus, the direct calcination of a CP at a temperature of 700 °C, which is above its decomposition temperature, yields ZnO.

In the present work, we demonstrate the effective application of water-soluble CPs as the precursors for the fabrication of hydrophobic ZnO nanostructures via the simple calcination route. The advantages of these CPs as precursors are simplicity of processing, reproducibility, scalability, and long-range ordering to get metal oxides with varied morphologies. Herein, we report the synthesis of 0D nanospheres, 1D microrods, and 3D polyhedra of ZnO by direct calcination of three different 1D Zn(II) CPs, with a general formula of {[Zn2(bpxa)2(adc)2]·xH2O}n (where bpxa = N,N-bis(pyridylmethyl)alkyl amine; adc = acetylene dicarboxylate; x = 0 or 2), at 700 °C.59 The three different ligands present in these CPs have a profound effect on the morphology of the obtained ZnO nanostructures as determined by the microscopic techniques and their photocatalytic activities. Furthermore, the three different kinetic theories (Elovich’s, intraparticle diffusion, and pseudo-second-order) were applied to model the experimental data for understanding the mechanism of sorption on the cationic methylene blue (MB) dye.

Results and Discussion

Synthesis and Characterization

The as-synthesized ZnO samples were named ZnO-bpxa-t (where bpxa = bpma, bpea, bpta and t = 6, 12, 18, 24 h). The use of 1D Zn(II) CPs has yielded ZnO nanostructures with high crystallinity and purity. Zn(II) CPs were calcined for different time intervals (6, 12, 18, and 24 h) in a tube furnace at 700 °C to get the ZnO nanostructures (Schemes 1–3), resulting in almost different morphologies in each case. The variation in morphology can be a result of some structural differences in the precursor polymers because of the change in the N-alkyl group from the methyl to ethyl to t-butyl group of the tridentate ligand in the CPs. Notably, the supramolecular interactions that are found in these CPs can be pointed out: moderate π–π interactions are present in [Zn2(bpea)2(adc)2]n but not in [Zn2(bpma)2(adc)2]n, whereas two lattice water molecules in {[Zn2(bpta)2(adc)2]·2H2O}n form a 2D supramolecular assembly by connecting two of its 1D CP chains.59 The formation of such nanostructures is remarkable without the use of any stabilizing agent. With a variation in the ligands of the precursors, these act as self-templating agents for the formation of different morphologies. Furthermore, the use of hydrothermal method followed by annealing of the same precursors provides different nanostructures as the mechanism of formation is different.60

Scheme 1. Synthesis of ZnO-bpma-6 to ZnO-bpma-24.

Scheme 1

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Scheme 3. Synthesis of ZnO-bpta-6 to ZnO-bpta-24.

Scheme 3

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Scheme 2. Synthesis of ZnO-bpea-6 to ZnO-bpea-24.

Scheme 2

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These are fully characterized by X-ray diffraction and microscopic and spectroscopic studies that are discussed in detail below. Figure 1 shows X-ray diffraction (XRD) patterns of the as-synthesized ZnO nanostructures with different retention times (6–24 h). All the peaks could be clearly indexed to the hexagonal wurtzite phase of ZnO, which matches well with the JCPDS card no of 36–1451. It is clear that the other form of ZnO, the cubic zinc blende, which can be found as the nucleus in the initiation of some nanostructures but is rather unstable, has quickly been transformed into the thermodynamically more stable wurtzite form under high-temperature calcination. The scattering from the (100), (002), and (101) planes can be clearly observed. There is no other characteristic peak for any impurity. This indicates high crystallinity and purity of the as-synthesized ZnO samples. The estimated lattice parameters, interplanar spacing (d), and atomic packing parameters for the hexagonal ZnO nanoparticles are shown in Table S1.61

Figure 1.

Figure 1

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Powder XRD patterns of the as-synthesized nanostructures: (a) ZnO-bpma-6 to ZnO-bpma-24, (b) ZnO-bpea-6 to ZnO-bpea-24, and (c) ZnO-bpta-6 to ZnO-bpta-24.

Microscopic Studies

Figure 2 shows the scanning electron microscopy (SEM) images of nanoparticles emerged after the heat treatment of [Zn2(bpma)2(adc)2]n to 700 °C for 6 h of retention time. As a result of spheroidizaton process, the necks and grain boundaries started emerging between these particles. These particles continued to grow with a little variation in size up to 18 h of retention time to form nanospheres and eventually get assembled to produce nanorods (80 nm) after 24 h of retention time. In general, phase composition and properties of the resulting daughter metal oxide nanostructures depend on the crystal structure of the parent CP. For example, two CPs composed of the same building blocks, Co2+ and 1,4-BDC, have plate- or rodlike structure of the parent CP. For example, two CPs composed of the same building blocks, Co2+ and 1,4-BDC, have plate- or rodlike morphologies (p-MOF and r-MOF), respectively.62 Accordingly, plate- and rodlike Co3O4 nanomaterials (p-Co3O4 and r-Co3O4, respectively) prepared via pseudomorphic conversion retained the morphology of the parent CP. In another study, superhydrophobic Zn(II) CP particles with controllable shapes were synthesized. Zinc oxides obtained from calcination of these CPs retain superhydrophobicity.56 In contrast, our study shows the utilization of 1D CPs as precursors, which should result in producing 1D nanostructures, but 0D nanospheres, 1D microrods, and 3D polyhedra (with a diamond-like structure) were obtained. Further, in our study, the hydrophobic ZnO nanostructures have been obtained from the hydrophilic water-soluble 1D CPs. In the present work, a complete transformation in the dimensionality as well as solubility has been obtained, which is remarkable.

Figure 2.

Figure 2

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FESEM images of (a) ZnO-bpma-6, (b) ZnO-bpma-12, (c) ZnO-bpma-18, (d) ZnO-bpma-24; € HRTEM image, (f,g) TEM images, and (h) SAED pattern of ZnO-bpta-12.

Furthermore, ZnO microrods were obtained with a change in precursor to [Zn2(bpea)2(adc)2]n, following the same procedure. After 6 h of retention, etching started from the top end of the microrods to overall erode downwards toward the c-axis, as shown in Figure 3a. As a result of fast etching from the corners, the tips started emerging from the top ends of the microrods. With the increase in the retention time from 6 to 12 h, the length of the tip increased. When the retention time was further extended to 18 h, a decrease in the length of the microrods was observed; however, the diameters from the top and bottom ends of the rods changed very little. Finally, after 24 h of retention, the tips started disappearing to produce rods with hexagonal ends. Thus, it can be concluded that the shortening of microrods was observed as a result of retention, which happens to be the dominant process instead of growth (Figure 3b-d).

Figure 3.

Figure 3

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FESEM images of (a) ZnO-bpea-6, (b) ZnO-bpea-12, (c) ZnO-bpea-18, (d) ZnO-bpea-24; (e–g) TEM images and (h) SAED pattern of ZnO-bpea-12.

When {[Zn2(bpta)2(adc)2]·2H2O}n was calcined to 6 h, ZnO nanoparticles grew up to 50–70 nm and assembled into nanoscale polyhedra, as shown in Figure 4a. With the elongation in time from 12 to 24 h, these nanoparticles continued to grow to produce nanoscale polyhedra with a diamond-like structure (Figure 4b–d).

Figure 4.

Figure 4

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FESEM images of (a) ZnO-bpta-6, (b) ZnO-bpta-12, (c) ZnO-bpta-18, (d) ZnO-bpta-24; (e) HRTEM image, (f,g) TEM images, and (h) SAED pattern of ZnO-bpta-12.

The formation of such nanostructure is remarkable without the use of a stabilizing agent. On the other hand, such a diamond-like structure of ZnO was obtained by refluxing the Zn(II) acetate precursor in tetraethylene glycol (TTEG) at 160 °C, where TTEG acts as a stabilizing agent.63 Based on the above results, the morphologies of nanostructures reported in this study are found to be precursor as well as time dependent (Table 1).

Table 1. Variation in the Morphology of ZnO Nanostructures Obtained in This Study.

time (h) precursor: [Zn2(bpma)2(adc)2]n precursor: [Zn2(bpea)2(adc)2]n precursor: [Zn2(bpta)2(adc)2]·2H2O]n
6 nanospheres (70–80 nm) microrod polyhedra (60–70 nm)
12 nanospheres (70–80 nm) microrod polyhedra (65–70 nm)
18 nanospheres (80–90 nm) microrod polyhedra (80–90 nm)
24 nanorods microrod polyhedra (80–90 nm)
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Figures 2f,g, 3f,g, and 4f,g show transmission electron microscopy (TEM) images of nanospheres (ZnO-bpma-12), microrods (ZnO-bpea-12), and polyhedra (ZnO-bpta-12) of ZnO nanostructures after 12 h of retention time. The nanospheres, microrods, and polyhedra are clearly visible in Figures 2f, 3f, and 4f. The high-resolution TEM (HRTEM) images (Figures 2e and 4e) show the distance of 0.22–0.26 nm between the lattice fringes of ZnO nanostructures coinciding with the distance between crystallographic planes of hexagonal wurtzite ZnO. The selected area electron diffraction (SAED) planes (100), (101), (001), and (002), as shown in Figures 2h, 3h, and 4h, confirm the results of XRD patterns. These results indicate that different frameworks of CPs mature finally to different morphologies (Figure 5).

Figure 5.

Figure 5

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Different morphologies (nanospheres, microrods, and polyhedra with a diamond-like structure) obtained as a result of change in the precursor.

Raman Spectroscopy

The Raman scattering spectra of the as-prepared ZnO nanostructures are shown in Figure S1 with 785 nm laser light as an excitation source. The wurtzite-phase ZnO, which belongs to the space-group P63mc group theory, predicts the existence of the following optic modes: Γopt = A1, E1, 2E2, 2B1.64 A1 and E1 are polar modes, whereas E2 mode is a nonpolar mode. All are Raman-active modes except two B1 modes, which are characterized as silent modes. The main dominant intense and sharp peak at around 436 cm–1 is assigned to E2 high mode of wurtzite ZnO, and the peak at 325 cm–1 is associated with the second-order Raman spectrum originating from the zone-boundary phonons.65 No peak at around 584 cm–1 was observed. This clearly indicates the absence of defects in the as-synthesized ZnO nanostructures.

Optical Properties

The room-temperature UV–visible absorption spectra of the as-synthesized ZnO nanostructures are shown in Figure S2. The absorption spectra showed a band around 380 nm corresponding to the formation of ZnO nanostructures. At this particular wavelength, a sharp decrease in the reflectance represents the uniform distribution of the particles in the nanostructures. The direct band gap energy (Eg) for the ZnO samples is determined from the graph of hν versus (αhν)2 for the absorption coefficient α, which is related to the band gap Eg as (αhν)2 = Ed(hν – Eg),66 where hν is the photon energy, and Ed is a constant. The extrapolation of the linear portion of the curve to absorption being equal to zero gives the value of band gap energy Eg. The inset in Figure S2 shows the band gap energies of the ZnO nanostructures. The band gap values of these nanostructures are given in Table S2. The average particle sizes of these nanostructures can be calculated from the absorption spectra by using the method proposed by Meulenkamp67

graphic file with name ao0c01555_m001.jpg 1

where a = 3.301, b = 294.0, and c = −1.09, λ1/2 (nm) is the wavelength at which absorption becomes half of that of the shoulder, and D (Å) is the diameter of the particle. The particle sizes of the as-synthesized ZnO nanostructures are given in Table S3.

Photoluminescence Studies

As a result of quantum confinement, the band gap energy of the materials increases, which can be clearly observed from the photoluminescence spectra for such materials. Further, the photocatalytic performance of the as-synthesized ZnO nanostructures is closely associated with the surface defects. The surface defects or the surface conditions can be effectively studied by measuring their optical properties. Figure 6a–c shows the photoluminescence spectrum of ZnO samples with an excitation wavelength of 320 nm at room temperature. All the samples showed a strong and broad emission band at around 395 nm, which corresponds to a near-band gap excitonic emission originating from the radiative recombination of excitons, whereas the emission band at around 508 nm in some of the nanostructures originates from deep-level transition in the surface defects.68 This emission is caused by the radiative recombination of charge carriers because of the oxygen vacancies and the interstitials of O and Zn atoms. High crystal quality can be observed in some of the nanostructures where only the UV emission is centered around 398 nm. Energy level diagrams for ZnO nanostructures are shown in Figure S3.

Figure 6.

Figure 6

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(a–c) Room-temperature photoluminescence spectra of the as-synthesized ZnO nanostructures.

Photocatalytic Activity

The MB dye was used as a contaminant in aqueous solution to study the photocatalytic activity of the as-synthesized ZnO nanostructures calcined for 12 h. Owing to the absorption in the visible region, MB has been extensively used as an indicator to verify the photocatalytic activities of the nanostructures. The characteristic absorption peak at 663 nm for MB is used to monitor the photocatalytic activities of the nanostructures. In this study, an aqueous solution of MB with a catalytic amount of ZnO sample is first kept in the dark for 30 min to achieve the absorption–desorption equilibrium, followed by an irradiation with UV light (Figure 7). With time evolution, the decolorization of MB was observed in terms of the change in intensity of λmax. The percentage of decolorization was calculated as follows69

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where A0 is the initial absorbance, and At is the absorbance after irradiation at various time intervals.

Figure 7.

Figure 7

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Absorption spectra of MB after adsorption in (a) ZnO-bpma-12, (b) ZnO-bpea-12, and (c) ZnO-bpta-12 for 8 h under UV light.

The photodegradation of MB can be considered as a Langmuir–Hinshelwood first-order kinetics reaction, which can be expressed as: ln(C0/C) = kt, where k is the reaction rate constant. A comparison of the adsorption behaviors of MB on the surface of ZnO samples is shown in Figure 8a. The decolorization of MB dye by ZnO nanostructures is shown in Figure 8b. The degradation ability and the rate constants of these nanostructures are shown in Table S4. It has been observed that polyhedra with a diamond-like structure (ZnO-bpta-12) displayed better efficiency in degrading the MB dye, followed by nanospheres (ZnO-bpma-12) and microrods (ZnO-bpea-12). In general, the degradation efficiency depends on many factors—surface area, particle, band gap, and so forth. The surface area for a given volume depends on the morphology of the particle. As a result, these different shaped nanostructures define the surface area for a given volume, which affects the photocatalytic activity. As a consequence of the isoperimetric inequality in all three dimensions for a nanosphere, it has the smaller surface area for a given volume. In contrast, polyhedra having a diamond-like structure with tiny spikes have larger surface area for a given volume. However, the rods with the size in micron range have smallest surface area for a given volume. Consequently, the photocatalytic degradation of MB follows the order of their surface areas: polyhedra with a diamond-like structure > nanospheres > microrods. A comparison of the degradation efficiencies of the as-synthesized ZnO nanostructures with similar materials reported in the literature is shown in Table S5.70−74 Although the rates are better in the literature reports, the present work shows a simple route to get variation in the dimensionality and solubility of the as-synthesized nanostructures using water-soluble 1D CPs, which is exceptional. We have also shown a correlation between the surface area of three different nanostructures and the degradation rates through this systematic study. It should be noted that MB-adsorbed nanomaterials can be reused and recycled easily by separating these from the reaction media by centrifugation and washing with ethanol. Thus, these are promising recyclable materials for environmental remediation.

Figure 8.

Figure 8

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(a) Comparison of photocatalytic degradation of MB over the as-synthesized ZnO catalysts, and (b) decolorization of MB by ZnO-bpma-12, ZnO-bpea-12, and ZnO-bpta-12 (labeled 1, 2, and 3).

Adsorption Dynamics

To identify the type of adsorption mechanism in order to determine the effectiveness of sorption of ZnO nanostructures onto the MB, three different models were studied to predict the adsorption kinetics75 of the as-synthesized ZnO nanostructures on MB. These kinetic models included Elovich’s, intraparticle diffusion, and pseudo-second-order.

Elovich’s Equation

It is used to describe the second-order kinetics, which involves the chemisorption process, but no specific mechanism for adsorbate–adsorbent can be proposed from the application of this equation. This model indicates how strong adsorbates are held on the surface of adsorbents.76,77 The linear form of the equation is proposed by Chien and Clayton,78 which can be expressed as follows

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where ae is the initial adsorption rate (mg/g min), and the parameter be is related to the extent of surface coverage and activation energy for chemisorption (g/mg). These constants can be obtained from the slope and intercept of the plot of qt versus ln(t). The plots of the samples fitted by this equation are shown in Figures S4, S7, and S10. The coefficient of regression values clearly indicates that the data are fitting well into this model (Table 2).

Table 2. Fitted Elovich’s Kinetic Model Parameters for the Removal of MB.
sample initial adsorption rate, ae (mg/g min) activation energy, be (g/mg) R2
ZnO-bpma-6 0.0174 0.6993 0.9799
ZnO-bpma-12 0.1016 0.6137 0.9714
ZnO-bpma-18 0.0709 0.7451 0.9576
ZnO-bpma-24 0.0152 1.7436 0.8867
ZnO-bpea-6 0.0155 1.4066 0.9151
ZnO-bpea-12 0.0181 1.1362 0.9433
ZnO-bpea-18 0.0169 1.7355 0.9783
ZnO-bpea-24 0.0092 1.6708 0.9463
ZnO-bpta-6 0.0144 2.9282 0.9708
ZnO-bpta-12 0.1886 2.4084 0.9873
ZnO-bpta-18 0.0265 2.1105 0.9835
ZnO-bpta-24 0.1362 2.3502 0.9932
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Intraparticle Diffusion Model

This model describes that the rate of adsorption process is controlled by the speed of diffusion of adsorbate into the adsorbent.79 The initial rate of intraparticle diffusion is given by Weber and Morris80 and can be expressed as

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A linear plot of qt versus t1/2, which passes through the origin, confirms the rate of adsorption controlled by this model. It is observed that other kinetic models may be operating when the plots does not pass through the origin. The plots of the samples fitted according to this model are shown in Figures S5, S8, and S11. The rate constant values and other fitting parameters are given in Table 3. From the correlation coefficients, it can be concluded that this model has a good agreement with the experimental data.

Table 3. Fitted Intraparticle Diffusion Kinetic Model Parameters for the Removal of MB.
sample rate constant, Ki (mg/g min1/2) intercept, C R2
ZnO-bpma-6 0.2075 0.1886 0.98983
ZnO-bpma-12 0.2367 0.5735 0.98353
ZnO-bpma-18 0.1963 0.2278 0.98587
ZnO-bpma-24 0.0740 –0.1240 0.96310
ZnO-bpea-6 0.1033 –0.5011 0.92722
ZnO-bpea-12 0.1179 –0.5315 0.97061
ZnO-bpea-18 0.0894 –03113 0.97081
ZnO-bpea-24 0.0880 –0.6432 0.98671
ZnO-bpta-6 0.0496 –0.0113 0.98950
ZnO-bpta-12 0.0590 0.9914 0.94946
ZnO-bpta-18 0.0687 0.1162 0.99412
ZnO-bpta-24 0.0603 0.8694 0.94961
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Pseudo-Second-Order

When the rate of sorption follows the second-order mechanism, the pseudo-second-order rate equation is represented by its linear form as shown below

graphic file with name ao0c01555_m005.jpg 5

where k2 is the rate constant of pseudo-second-order adsorption (g/mg min), and qt (mg/g) is the amount of adsorbate retained at time (t). The initial adsorption rate, h, (mg/g min) is expressed as

graphic file with name ao0c01555_m006.jpg 6

If the plot of t/qt versus t gives a linear relationship, the constants k2 and h can be determined from the intercept and slope of the line obtained from the plot. The surface adsorption involving chemisorption is the rate-limiting step for this process.81,82 The removal of the dye from the aqueous solution is because of the physicochemical interactions between the phases. Figures S6, S9, and S12 show the plot fitted using this model. The regression values confirm fitting of the data into this model, as shown in Table 4. Because the experimental data fit well into all the three kinetic models, it can be concluded that the adsorption of the dye by ZnO nanostructures occurs simultaneously by all of them, but the rate of adsorption is maximum in the intraparticle diffusion model.

Table 4. Fitted Pseudo-Second-Order Kinetic Model Parameters for the Removal of MB.
sample initial adsorption rate, h (mg/g min) rate constant, K2 (g/mg) R2
ZnO-bpma-6 0.0343 0.000864 0.9848
ZnO-bpma-12 0.0476 0.000893 0.9845
ZnO-bpma-18 0.0332 0.000919 0.9712
ZnO-bpma-24 0.0059 0.000516 0.9756
ZnO-bpea-6 0.0083 0.002217 0.9227
ZnO-bpea-12 0.00958 0.00132 0.9923
ZnO-bpea-18 0.00603 0.000544 0.9940
ZnO-bpea-24 0.00385 0.003342 0.9923
ZnO-bpta-6 0.0069 0.003064 0.9827
ZnO-bpta-12 0.0431 0.007101 0.9965
ZnO-bpta-18 0.0126 0.002851 0.9876
ZnO-bpta-24 0.0385 0.006844 0.9989
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Conclusions

This work presented the utilization of CPs as suitable precursors for the synthesis of ZnO nanostructures in a short time. The three different ligands around the Zn(II) metal center showed a profound effect on the morphologies, sizes, optical properties, and photocatalytic activities of the as-synthesized ZnO nanostructures. The water-soluble 1D CPs resulted in producing hydrophobic 0D nanospheres, 1D microrods, and 3D polyhedra. Different retention times in the synthesis can control the growth kinetics and vary the shapes and the physicochemical properties of ZnO nanostructures. The calculated average sizes of the ZnO nanostructures were found to be in the range of 55–75 nm. A sharp UV band around 390 nm, corresponding to near-band gap emission and broad green emission because of oxygen vacancies around 520 nm in ZnO nanostructures, was also observed. From the photocatalytic studies of MB, it can be concluded that the rate of degradation was found to be faster for ZnO polyhedra with the retention time of 12 h. The percent degradation of MB using the ZnO catalysts follows the order: ZnO-bpta-12 > ZnO-bpma-12 > ZnO-bpea-12. The results reveal that the intraparticle diffusion model exhibits the maximum rate of adsorption among all the kinetic models.

Experimental Section

Materials and Methods

All chemicals for synthesis were purchased commercially and used as received without further purification. All reactions were carried out under aerobic conditions. All CPs used in this study were prepared in gram quantities following the literature method.59

Physical Measurements

Powder X-ray diffraction was carried out with a Rigaku Ultima IV diffractometer that was equipped with a 3 kW sealed tube with Cu Kα X-ray radiation (generator power settings: 40 kV and 40 mA) and a DTex Ultra detector choosing the option for the Bragg Brentano geometry (2.5° primary and secondary solar slits and 0.5° divergence slit with 10 mm height limit slit). Each properly ground sample was placed on a glass sample holder that was placed on the sample stage for data collection between 2θ values of 5–80° with a scanning speed of 2° per min. For the morphology and chemical composition of the as-synthesized samples, data were collected and analyzed by field-emission SEM (FESEM, JEOL, 15 kV) and energy-dispersive X-ray spectroscopy (EDX, HORIBA EX-250, 15 kV) associated with FESEM. For TEM of the as-synthesized samples, an FEI Tecnai G2 F20 instrument equipped with a field emission gun operated at 200 kV was used; in each case, a copper grid was appropriately loaded using 1 mg of sample (well dispersed in 10 mL of ethanol with the help of a sonicator for 20 min). Solid-state diffuse reflectance spectra were recorded using a Cary 5000 UV–vis–NIR spectrophotometer by Agilent Technology with a KBr solid-state holder. Solid-state fluorescence spectra were obtained using a HORIBA Fluorolog 3 spectrofluorometer. Each data set was analyzed with FluorEssence software. Photocatalytic experiments were carried out using a spectroline 8 W UV lamp.

Preparation of ZnO Nanostructures

For the synthesis of ZnO nanostructures, a conventional horizontal tube furnace composed of an alumina tube, a rotary pump system, a gas supply, and a control system was used. About 0.05 mmol of the source material, that is, Zn(II) polymers ([Zn2(bpma)2(adc)2]n (39 mg), [Zn2(bpea)2(adc)2]n (40 mg), and {[Zn2(bpta)2(adc)2]·2H2O}n (45 mg) were taken in silica crucibles and loaded on an alumina boat and positioned at the center of the tube to get the maximum temperature. The temperature of the source material was set at 700 °C, and the heating was maintained at the rate of 3 °C/min. After attaining this temperature, it was maintained for different times 6, 12, 18, and 24 h. The furnace was then allowed to cool with the same rate. The white powders were collected in each case.

Photocatalytic Measurements

The cationic dye MB was chosen to examine the photocatalytic performance of the as-synthesized nanostructures. A spectroline 8 W UV lamp (λ = 365 nm) was used as the light source. The as-synthesized nanostructures (5 mg) were dispersed into 10 mL of a 0.94 mM solution of MB (30 mg in 100 mL water) and vigorously stirred in the dark for 30 min to reach the adsorption–desorption equilibrium between the samples and MB at room temperature. During illumination under an UV lamp, the aliquots of about 2 mL were collected and centrifuged at fixed time intervals. The concentration of MB was analyzed at given intervals by a Cary 60 UV–vis spectrophotometer.

Adsorption Kinetics

To study the kinetics of adsorption, the experimental data were fitted into suitable rate expressions to estimate the possible reaction mechanisms and the rates of adsorption of the ZnO nanostructures on the surface of MB. Thus, it becomes important to model the adsorption rates to analyze the adsorption dynamics and to establish the time dependence of these adsorption systems. Several mechanistic models have been studied to describe the adsorption kinetics effectively such as film diffusion, intraparticle diffusion, pseudo kinetic model, Elovich’s model, film solid model, and the film pore model.83−88 In the present study, an extensive analysis on three kinetic models (pseudo-second-order model, Elovich’s model, and intraparticle diffusion model) was made to have a better understanding of the adsorption kinetics.

Acknowledgments

Funding for this work was provided by IISER Mohali. S.T. is grateful to MHRD of India for a research fellowship. The use of X-ray and FESEM facilities at IISER Mohali, and TEM facility at NIPER Mohali, is gratefully acknowledged.

Supporting Information Available

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsomega.0c01555.

  • Lattice parameters and band gap values of the as-synthesized ZnO nanostructures, calculated particle sizes of the as-synthesized ZnO nanostructures using Meulenkamp’s equation, percent decolorization and rate constant values of the as-synthesized ZnO nanostructures calcined for 12 hours, comparison of percentage degradation efficiency of MB dye by the ZnO nanostructures with literature values, Raman spectra of ZnO nanostructures, Tauc plots of the as-synthesized ZnO nanostructures, energy level diagram of the as-synthesized ZnO nanostructures, and Linear fit of kinetic models (PDF)

The authors declare no competing financial interest.

Supplementary Material

ao0c01555_si_001.pdf (2MB, pdf)

References

  1. Djurišić A. B.; Ng A. M. C.; Chen X. Y. ZnO Nanostructures for Optoelectronics: Material Properties and Device Applications. Prog. Quant. Electron. 2010, 34, 191–259. 10.1016/j.pquantelec.2010.04.001. [DOI] [Google Scholar]
  2. Biasotto G.; Ranieri M. G. A.; Foschini C. R.; Simões A. Z.; Longo E.; Zaghete M. A. Gas Sensor Applications of Zinc Oxide Thin Film Grown by the Polymeric Precursor Method. Ceram. Int. 2014, 40, 14991–14996. 10.1016/j.ceramint.2014.06.099. [DOI] [Google Scholar]
  3. Li G.; Jiang Y.; Zhang Y.; Lan X.; Zhai T.; Yi G.-C. High-Performance Photodetectors and Enhanced Field-Emission of CdS Nanowire Arrays on CdSe Single-Crystalline Sheets. J. Mater. Chem. C 2014, 2, 8252–8258. 10.1039/c4tc01503g. [DOI] [Google Scholar]
  4. Anta J. A.; Guillén E.; Tena-Zaera R. ZnO-Based Dye-Sensitized Solar Cells. J. Phys. Chem. C 2012, 116, 11413–11425. 10.1021/jp3010025. [DOI] [Google Scholar]
  5. Tayebee R.; Nasr A. H.; Rabiee S.; Adibi E. Zinc Oxide as a Useful and Recyclable Catalyst for the One-Pot Synthesis of 2,4,6-Trisubstituted-1,3,5-Trioxanes under Solvent-Free Conditions. Ind. Eng. Chem. Res. 2013, 52, 9538–9543. 10.1021/ie401562j. [DOI] [Google Scholar]
  6. Khalafi T.; Buazar F.; Ghanemi K. Phycosynthesis and Enhanced Photocatalytic Activity of Zinc Oxide Nanoparticles Toward Organosulfur Pollutants. Sci. Rep. 2019, 9, 6866. 10.1038/s41598-019-43368-3. [DOI] [PMC free article] [PubMed] [Google Scholar]
  7. Elango G.; Roopan S. M. Efficacy of SnO2 Nanoparticles toward Photocatalytic Degradation of Methylene Blue Dye. J. Photochem. Photobiol. B Biol. 2016, 155, 34–38. 10.1016/j.jphotobiol.2015.12.010. [DOI] [PubMed] [Google Scholar]
  8. Mahmoud W. M. M.; Rastogi T.; Kümmerer K. Application of Titanium Dioxide Nanoparticles as a Photocatalyst for the Removal of Micropollutants Such as Pharmaceuticals from Water. Curr. Opin. Green Sustain. Chem. 2017, 16, 1–10. 10.1016/j.cogsc.2017.04.001. [DOI] [Google Scholar]
  9. Reddy C. V.; Babu B.; Reddy I. N.; Shim J. Synthesis and Characterization of Pure Tetragonal ZrO2 Nanoparticles with Enhanced Photocatalytic Activity. Ceram. Int. 2018, 44, 6940–6948. 10.1016/j.ceramint.2018.01.123. [DOI] [Google Scholar]
  10. Prabhu S.; Megala S.; Harish S.; Navaneethan M.; Maadeswaran P.; Sohila S.; Ramesh R. Enhanced Photocatalytic Activities of ZnO Dumbbell/Reduced Graphene Oxide Nanocomposites for Degradation of Organic Pollutants via Efficient Charge Separation Pathway. Appl. Surf. Sci. 2019, 487, 1279–1288. 10.1016/j.apsusc.2019.05.086. [DOI] [Google Scholar]
  11. Moussa H.; Chouchene B.; Gries T.; Balan L.; Mozet K.; Medjahdi G.; Schneider R. Growth of ZnO Nanorods on Graphitic Carbon Nitride gCN Sheets for the Preparation of Photocatalysts with High Visible-Light Activity. ChemCatChem 2018, 10, 4973–4983. 10.1002/cctc.201801206. [DOI] [Google Scholar]
  12. Umar A.; Akhtar M. S.; Al-Hajry A.; Al-Assiri M. S.; Almehbad N. Y. Hydrothermally Grown ZnO Nanoflowers for Environmental Remediation and Clean Energy Applications. Mater. Res. Bull. 2012, 47, 2407–2414. 10.1016/j.materresbull.2012.05.028. [DOI] [Google Scholar]
  13. Mohammad A.; Kapoor K.; Mobin S. M. Improved Photocatalytic Degradation of Organic Dyes by ZnO-Nanoflowers. ChemistrySelect 2016, 1, 3483–3490. 10.1002/slct.201600476. [DOI] [Google Scholar]
  14. Srikant V.; Clarke D. R. On the Optical Band Gap of Zinc Oxide. J. Appl. Phys. 1998, 83, 5447–5451. 10.1063/1.367375. [DOI] [Google Scholar]
  15. Keis K.; Bauer C.; Boschloo G.; Hagfeldt A.; Westermark K.; Rensmo H.; Siegbahn H. Nanostructured ZnO Electrodes for Dye-Sensitized Solar Cell Applications. J. Photochem. Photobiol. A Chem. 2002, 148, 57–64. 10.1016/s1010-6030(02)00039-4. [DOI] [Google Scholar]
  16. Kołodziejczak-Radzimska A.; Jesionowski T. Zinc Oxide-from Synthesis to Application: A Review. Materials 2014, 7, 2833–2881. 10.3390/ma7042833. [DOI] [PMC free article] [PubMed] [Google Scholar]
  17. Pelicano C. M.; Yanagi H. Efficient Solid-State Perovskite Solar Cells Based on Nanostructured Zinc Oxide Designed by Strategic Low Temperature Water Oxidation. J. Mater. Chem. C 2017, 5, 8059–8070. 10.1039/c7tc01934c. [DOI] [Google Scholar]
  18. Prosa M.; Tessarolo M.; Bolognesi M.; Margeat O.; Gedefaw D.; Gaceur M.; Videlot-Ackermann C.; Andersson M. R.; Muccini M.; Seri M.; et al. Enhanced Ultraviolet Stability of Air-Processed Polymer Solar Cells by Al Doping of the ZnO Interlayer. ACS Appl. Mater. Interfaces 2016, 8, 1635–1643. 10.1021/acsami.5b08255. [DOI] [PubMed] [Google Scholar]
  19. Zhao B.; Wang F.; Chen H.; Wang Y.; Jiang M.; Fang X.; Zhao D. Solar-Blind Avalanche Photodetector Based on Single ZnO-Ga2O3 Core-Shell Microwire. Nano Lett. 2015, 15, 3988–3993. 10.1021/acs.nanolett.5b00906. [DOI] [PubMed] [Google Scholar]
  20. Yang R.; Yan X.; Li Y.; Zhang X.; Chen J. Nitrogen-Doped Porous Carbon-ZnO Nanopolyhedra Derived from ZIF-8: New Materials for Photoelectrochemical Biosensors. ACS Appl. Mater. Interfaces 2017, 9, 42482–42491. 10.1021/acsami.7b10856. [DOI] [PubMed] [Google Scholar]
  21. Veerla R. S.; Sahatiya P.; Badhulika S. Fabrication of a Flexible UV Photodetector and Disposable Photoresponsive Uric Acid Sensor by Direct Writing of ZnO Pencil on Paper. J. Mater. Chem. C 2017, 5, 10231–10240. 10.1039/c7tc03292g. [DOI] [Google Scholar]
  22. Gupta T. K. Application of Zinc Oxide Varistors. J. Am. Ceram. Soc. 1990, 73, 1817–1840. 10.1111/j.1151-2916.1990.tb05232.x. [DOI] [Google Scholar]
  23. Djurišić A. B.; Chen X.; Leung Y. H.; Man Ching Ng A. ZnO Nanostructures: Growth, Properties and Applications. J. Mater. Chem. 2012, 22, 6526–6535. 10.1039/c2jm15548f. [DOI] [Google Scholar]
  24. Li X.; Song J.; Liu Y.; Zeng H. Controlling Oxygen Vacancies and Properties of ZnO. Curr. Appl. Phys. 2014, 14, 521–527. 10.1016/j.cap.2014.01.007. [DOI] [Google Scholar]
  25. Bahuguna A.; Kumar S.; Krishnan V. Nanohybrid of ZnO-RGO as Heterogeneous Green Catalyst for the Synthesis of Medicinally Significant Indole Alkaloids and Their Derivatives. ChemistrySelect 2018, 3, 314–320. 10.1002/slct.201701990. [DOI] [Google Scholar]
  26. Pauporté T.; Lincot D. Electrodeposition of Semiconductors for Optoelectronic Devices: Results on Zinc Oxide. Electrochim. Acta 2000, 45, 3345–3353. 10.1016/s0013-4686(00)00405-9. [DOI] [Google Scholar]
  27. Yang K.; She G.-W.; Wang H.; Ou X.-M.; Zhang X.-H.; Lee C.-S.; Lee S.-T. ZnO Nanotube Arrays as Biosensors for Glucose. J. Phys. Chem. B 2009, 113, 20169–20172. 10.1021/jp901894j. [DOI] [Google Scholar]
  28. Kuo C.-L.; Kuo T.-J.; Huang M. H. Hydrothermal Synthesis of ZnO Microspheres and Hexagonal Microrods with Sheetlike and Platelike Nanostructures. J. Mater. Chem. C 2005, 109, 20115–20121. 10.1021/jp0528919. [DOI] [PubMed] [Google Scholar]
  29. Zheng F.; Lu H.; Guo M.; Zhang M.; Zhen Q. Hydrothermal Preparation of WO3 Nanorod Array and ZnO Nanosheet Array Composite Structures on FTO Substrates with Enhanced Photocatalytic Properties. J. Mater. Chem. C 2015, 3, 7612–7620. 10.1039/c5tc01125f. [DOI] [Google Scholar]
  30. Gao T.; Li Q.; Wang T. Sonochemical Synthesis, Optical Properties, and Electrical Properties of Core/Shell-Type ZnO Nanorod/CdS Nanoparticle Composites. Chem. Mater. 2005, 17, 887–892. 10.1021/cm0485456. [DOI] [Google Scholar]
  31. Nistor S. V.; Nistor L. C.; Stefan M.; Ghica D.; Aldica G.; Barascu J. N. Crystallization of Disordered Nanosized ZnO Formed by Thermal Decomposition of Nanocrystalline Hydrozincite. Cryst. Growth Des. 2011, 11, 5030–5038. 10.1021/cg2009286. [DOI] [Google Scholar]
  32. Oliveira A. P. A.; Hochepied J.-F.; Grillon F.; Berger M.-H. Controlled Precipitation of Zinc Oxide Particles at Room Temperature. Chem. Mater. 2003, 15, 3202–3207. 10.1021/cm0213725. [DOI] [Google Scholar]
  33. Zdujić M. V.; Milošević O. B.; Karanović L. Č. Mechanochemical Treatment of ZnO and Al2O3 Powders by Ball Milling. Mater. Lett. 1992, 13, 125–129. 10.1016/0167-577x(92)90122-z. [DOI] [Google Scholar]
  34. Lim S. K.; Hwang S.-H.; Kim S.; Park H. Preparation of ZnO Nanorods by Microemulsion Synthesis and Their Application as a CO Gas Sensor. Sens. Actuat. B 2011, 160, 94–98. 10.1016/j.snb.2011.07.018. [DOI] [Google Scholar]
  35. Kaneti Y. V.; Yue J.; Jiang X.; Yu A. Controllable Synthesis of ZnO Nanoflakes with Exposed (101−0) for Enhanced Gas Sensing Performance. J. Phys. Chem. C 2013, 117, 13153–13162. 10.1021/jp404329q. [DOI] [Google Scholar]
  36. Reda S. M. Synthesis of ZnO and Fe2O3 Nanoparticles by Solgel Method and Their Application in Dye-Sensitized Solar Cells. Mater. Sci. Semicond. Process. 2010, 13, 417–425. 10.1016/j.mssp.2011.09.007. [DOI] [Google Scholar]
  37. Zhu Z.; Chen T.-L.; Gu Y.; Warren J.; Osgood R. M. Zinc Oxide Nanowires Grown by Vapor-Phase Transport Using Selected Metal Catalysts: A Comparative Study. Chem. Mater. 2005, 17, 4227–4234. 10.1021/cm050584+. [DOI] [Google Scholar]
  38. Fazio E.; Mezzasalma A. M.; Mondio G.; Neri F.; Saija R. ZnO Nanostructures Produced by Laser Ablation in Water: Optical and Structural Properties. Appl. Surf. Sci. 2013, 272, 30–35. 10.1016/j.apsusc.2012.03.087. [DOI] [Google Scholar]
  39. Gondal M. A.; Drmosh Q. A.; Yamani Z. H.; Saleh T. A. Synthesis of ZnO2 nanoparticles by laser ablation in liquid and their annealing transformation into ZnO nanoparticles. Appl. Surf. Sci. 2009, 256, 298–304. 10.1016/j.apsusc.2009.08.019. [DOI] [Google Scholar]
  40. Jung S.; Cho W.; Lee H. J.; Oh M. Self-Template-Directed Formation of Coordination-Polymer Hexagonal Tubes and Rings, and their Calcination to ZnO Rings. Angew. Chemie 2009, 121, 1487–1490. 10.1002/ange.200804816. [DOI] [PubMed] [Google Scholar]
  41. Cho W.; Lee Y. H.; Lee H. J.; Oh M. Systematic Transformation of Coordination Polymer Particles to Hollow and Non-Hollow In2O3 with Pre-Defined Morphology. Chem. Commun. 2009, 31, 4756–4758. 10.1039/b907281k. [DOI] [PubMed] [Google Scholar]
  42. Li C.; Yin X.; Chen L.; Li Q.; Wang T. Synthesis of Cobalt Ion-Based Coordination Polymer Nanowires and Their Conversion into Porous Co3O4 Nanowires with Good Lithium Storage Properties. Chem.—Eur. J. 2010, 16, 5215–5221. 10.1002/chem.200901632. [DOI] [PubMed] [Google Scholar]
  43. Sikora B.; Fronc K.; Kamińska I.; Koper K.; Stępień P.; Elbaum D. Luminescence of Colloidal ZnO Nanoparticles Synthesized in Alcohols and Biological Application of ZnO Passivated by MgO. J. Phys. Condens. Matter 2013, 25, 194104. 10.1088/0953-8984/25/19/194104. [DOI] [PubMed] [Google Scholar]
  44. Nishad K. K.; Pandey R. K. Size Dependent Ferromagnetism in Dodecyl Amine Capped ZnO Nanoparticles. Mater. Sci. Eng. B Solid-State Mater. Adv. Technol. 2013, 178, 1380–1389. 10.1016/j.mseb.2013.08.002. [DOI] [Google Scholar]
  45. Zhou G.; Li Y.; Ma Y.; Liu Z.; Cao L.; Wang D.; Liu S.; Xu W.; Wang W. Size-Dependent Cytotoxicity of Yttrium Oxide Nanoparticles on Primary Osteoblasts in Vitro. J. Nanoparticle Res. 2016, 18, 1–14. 10.1007/s11051-016-3447-5. [DOI] [Google Scholar]
  46. Talebian N.; Amininezhad S. M.; Doudi M. Controllable Synthesis of ZnO Nanoparticles and Their Morphology-Dependent Antibacterial and Optical Properties. J. Photochem. Photobiol. B Biol. 2013, 120, 66–73. 10.1016/j.jphotobiol.2013.01.004. [DOI] [PubMed] [Google Scholar]
  47. Bacsa R. R.; Dexpert-Ghys J.; Verelst M.; Falqui A.; Machado B.; Bacsa W. S.; Chen P.; Zakeeruddin S. M.; Graetzel M.; Serp P. Synthesis and Structure-Property Correlation in Shape-Controlled ZnO Nanoparticles Prepared by Chemical Vapor Synthesis and their Application in Dye-Sensitized Solar Cells. Adv. Funct. Mater. 2009, 19, 875–886. 10.1002/adfm.200801049. [DOI] [Google Scholar]
  48. Mirtamizdoust B.; Bieńko D. C.; Hanifehpour Y.; Tiekink E. R. T.; Yilmaz V. T.; Talemi P.; Joo S. W. Preparation of a Novel Nano-Scale Lead(II) Zig-Zag Metal–Organic Coordination Polymer with Ultrasonic Assistance: Synthesis, Crystal Structure, Thermal Properties, and NBO Analysis of [Pb(μ-2-Pinh)N3 H2O]n. J. Inorg. Organomet. Polym. Mater. 2016, 26, 819–828. 10.1007/s10904-016-0385-8. [DOI] [Google Scholar]
  49. Aghabeygi S.; Bigdeli F.; Morsali A. Synthesis and Characterization of Zinc(II) Oxide Nanoparticles by Thermal Decomposition of Two Zinc(II) Nitrite Coordination Polymer Precursors. J. Inorg. Organomet. Polym. Mater. 2012, 22, 526–529. 10.1007/s10904-011-9575-6. [DOI] [Google Scholar]
  50. Xu X.; Cao R.; Jeong S.; Cho J. Spindle-like Mesoporous α-Fe2O3 Anode Material Prepared from MOF Template for High-Rate Lithium Batteries. Nano Lett. 2012, 12, 4988–4991. 10.1021/nl302618s. [DOI] [PubMed] [Google Scholar]
  51. Zhang F.; Qi D.-D.; Zhang X.-G. Synthesis and Lithium Storage Performance of Mesoporous Co3O4 Microrods Derived From Co-Based Metal-Organic Framework. Int. J. Electrochem. Sci. 2016, 11, 189–199. [Google Scholar]
  52. Wu R.; Qian X.; Yu F.; Liu H.; Zhou K.; Wei J.; Huang Y. MOF-Templated Formation of Porous CuO Hollow Octahedra for Lithium-Ion Battery Anode Materials. J. Mater. Chem. A 2013, 1, 11126–11129. 10.1039/c3ta12621h. [DOI] [Google Scholar]
  53. Zhang S.; Liu H.; Sun C.; Liu P.; Li L.; Yang Z.; Feng X.; Huo F.; Lu X. CuO/Cu2O Porous Composites: Shape and Composition Controllable Fabrication Inherited from Metal Organic Frameworks and Further Application in CO Oxidation. J. Mater. Chem. A 2015, 3, 5294–5298. 10.1039/c5ta00249d. [DOI] [Google Scholar]
  54. Moeinian M.; Akhbari K. Various Methods for Synthesis of Bulk and Nano Thallium(III) Oxide. J. Inorg. Organomet. Polym. Mater. 2016, 26, 1–13. 10.1007/s10904-015-0289-z. [DOI] [Google Scholar]
  55. Jung S.; Cho W.; Lee H. J.; Oh M. Self-Template-Directed Formation of Coordination-Polymer Hexagonal Tubes and Rings, and their Calcination to ZnO Rings. Angew. Chem., Int. Ed. Engl. 2009, 48, 1459–1462. 10.1002/anie.200804816. [DOI] [PubMed] [Google Scholar]
  56. Lu Y.; Cao H.; Zhang S.; Zhang X. Shape Controlled Synthesis of Superhydrophobic Zinc Coordination Polymers Particles and Their Calcination to Superhydrophobic ZnO. J. Mater. Chem. 2011, 21, 8633–8639. 10.1039/c1jm10957j. [DOI] [Google Scholar]
  57. Bigdeli F.; Morsali A. Synthesis ZnO Nanoparticles from a New Zinc(II) Coordination Polymer Precursor. Mater. Lett. 2010, 64, 4–5. 10.1016/j.matlet.2009.09.038. [DOI] [Google Scholar]
  58. Lee K. J.; Lee J. H.; Jeoung S.; Moon H. R. Transformation of Metal-Organic Frameworks/Coordination Polymers into Functional Nanostructured Materials: Experimental Approaches Based on Mechanistic Insights. Acc. Chem. Res. 2017, 50, 2684–2692. 10.1021/acs.accounts.7b00259. [DOI] [PubMed] [Google Scholar]
  59. Khullar S.; Mandal S. K. Non-Hydrothermal Synthesis, Structural Characterization and Thermochemistry of Water Soluble and Neutral Coordination Polymers of Zn(II) and Cd(II): Precursors for the Submicron-Sized Crystalline ZnO/CdO. RSC Adv. 2014, 4, 39204–39213. 10.1039/c4ra03928a. [DOI] [Google Scholar]
  60. Thakur S.; Mandal S. K. Effect of Dilution in a Hydrothermal Process and Post-Synthetic Annealing on the Tailoring of Hierarchical ZnO Nanostructures. CrystEngComm 2020, 22, 3059–3069. 10.1039/d0ce00310g. [DOI] [Google Scholar]
  61. Prakash T.; Neri G.; Bonavita A.; Ranjith Kumar E.; Gnanamoorthi K. Structural, Morphological and Optical Properties of Bi-Doped ZnO Nanoparticles Synthesized by a Microwave Irradiation Method. J. Mater. Sci. Mater. Electron. 2015, 26, 4913–4921. 10.1007/s10854-015-3002-7. [DOI] [Google Scholar]
  62. Lee K. J.; Kim T.-H.; Kim T. K.; Lee J. H.; Song H.-K.; Moon H. R. Preparation of Co3O4 Electrode Materials with Different Microstructures via Pseudomorphic Conversion of Co-Based Metal-Organic Frameworks. J. Mater. Chem. A 2014, 2, 14393–14400. 10.1039/c4ta02501f. [DOI] [Google Scholar]
  63. Chieng B. W.; Loo Y. Y. Synthesis of ZnO Nanoparticles by Modified Polyol Method. Mater. Lett. 2012, 73, 78–82. 10.1016/j.matlet.2012.01.004. [DOI] [Google Scholar]
  64. Bergman L.; Chen X. B.; Huso J.; Morrison J. L.; Hoeck H. Raman Scattering of Polar Modes of ZnO Crystallites. J. Appl. Phys. 2005, 98, 093507. 10.1063/1.2126784. [DOI] [Google Scholar]
  65. Alim K. A.; Fonoberov V. A.; Shamsa M.; Balandin A. A. Micro-Raman Investigation of Optical Phonons in ZnO Nanocrystals. J. Appl. Phys. 2005, 97, 124313. 10.1063/1.1944222. [DOI] [Google Scholar]
  66. Kamarulzaman N.; Kasim M. F.; Rusdi R. Band Gap Narrowing and Widening of ZnO Nanostructures and Doped Materials. Nanoscale Res. Lett. 2015, 10, 346. 10.1186/s11671-015-1034-9. [DOI] [PMC free article] [PubMed] [Google Scholar]
  67. Meulenkamp E. A. Synthesis and Growth of ZnO Nanoparticles. J. Phys. Chem. B 1998, 102, 5566–5572. 10.1021/jp980730h. [DOI] [Google Scholar]
  68. Willander M.; Nur O.; Sadaf J. R.; Qadir M. I.; Zaman S.; Zainelabdin A.; Bano N.; Hussain I. Luminescence from Zinc Oxide Nanostructures and Polymers and Their Hybrid Devices. Materials 2010, 3, 2643–2667. 10.3390/ma3042643. [DOI] [Google Scholar]
  69. Li S.; Lin Q.; Liu X.; Yang L.; Ding J.; Dong F.; Li Y.; Irfan M.; Zhang P. Fast Photocatalytic Degradation of Dyes Using Low-Power Laser-Fabricated Cu2O−Cu Nanocomposites. RSC Adv. 2018, 8, 20277–20286. 10.1039/C8RA03117G. [DOI] [PMC free article] [PubMed] [Google Scholar]
  70. Balcha A.; Yadav O. P.; Dey T. Photocatalytic Degradation of Methylene Blue Dye by Zinc Oxide Nanoparticles Obtained from Precipitation and Sol-Gel Methods. Environ. Sci. Pollut. Res. 2016, 23, 25485–25493. 10.1007/s11356-016-7750-6. [DOI] [PubMed] [Google Scholar]
  71. Jain N.; Bhargava A.; Panwar J. Enhanced photocatalytic degradation of methylene blue using biologically synthesized ″protein-capped″ ZnO nanoparticles. Chem. Eng. J. 2014, 243, 549–555. 10.1016/j.cej.2013.11.085. [DOI] [Google Scholar]
  72. Lu H.; Li X.; Zhang Z.; Shao G. One-Step Microwave Synthesis of Ag/ZnO Microrods as Photocatalysts. Mater. Res. Innov. 2019, 23, 129–134. 10.1080/14328917.2017.1395979. [DOI] [Google Scholar]
  73. Isai K. A.; Shrivastava V. S. Photocatalytic Degradation of Methylene Blue Using ZnO and 2%Fe–ZnO Semiconductor Nanomaterials Synthesized by Sol–Gel Method: A Comparative Study. SN Appl. Sci. 2019, 4, 1247. [Google Scholar]
  74. Anju Chanu L.; Joychandra Singh W.; Jugeshwar Singh K.; Nomita Devi K. Effect of Operational Parameters on the Photocatalytic Degradation of Methylene Blue Dye Solution Using Manganese Doped ZnO Nanoparticles. Results Phys. 2019, 12, 1230–1237. 10.1016/j.rinp.2018.12.089. [DOI] [Google Scholar]
  75. Chang C.-H.; Franses E. I. Adsorption Dynamics of Surfactants at the Air/Water Interface: A Critical Review of Mathematical Models, Data, and Mechanisms. Colloids Surf. A Physicochem. Eng. Asp. 1995, 100, 1–45. 10.1016/0927-7757(94)03061-4. [DOI] [Google Scholar]
  76. Farouq R.; Yousef N. S.; Yousef N. S. Equilibrium and Kinetics Studies of Adsorption of Copper (II) Ions on Natural Biosorbent. Int. J. Chem. Eng. Appl. 2015, 6, 319–324. 10.7763/ijcea.2015.v6.503. [DOI] [Google Scholar]
  77. Ho Y. S.; McKay G. Application of Kinetic Models to the Sorption of Copper(II) on to Peat. Adsorpt. Sci. Technol. 2002, 20, 797–815. 10.1260/026361702321104282. [DOI] [Google Scholar]
  78. Chien S. H.; Clayton W. R. Application of Elovich Equation to the Kinetics of Phosphate Release and Sorption in Soils. Soil Sci. Soc. Am. J. 1980, 44, 265–268. 10.2136/sssaj1980.03615995004400020013x. [DOI] [Google Scholar]
  79. Wu F.-C.; Tseng R.-L.; Juang R.-S. Initial Behavior of Intraparticle Diffusion Model Used in the Description of Adsorption Kinetics. Chem. Eng. J. 2009, 153, 1–8. 10.1016/j.cej.2009.04.042. [DOI] [Google Scholar]
  80. Weber W. J.; Morris J. C. Kinetics of Adsorption on Carbon From Solution. J. Sanit. Eng. Div. 1963, 89, 31–60. [Google Scholar]
  81. Miyake Y.; Ishida H.; Tanaka S.; Kolev S. D. Theoretical Analysis of the Pseudo-Second Order Kinetic Model of Adsorption. Application to the Adsorption of Ag(I) to Mesoporous Silica Microspheres Functionalized with Thiol Groups. Chem. Eng. J. 2013, 218, 350–357. 10.1016/j.cej.2012.11.089. [DOI] [Google Scholar]
  82. Wu F.-C.; Tseng R.-L.; Huang S.-C.; Juang R.-S. Characteristics of Pseudo-Second-Order Kinetic Model for Liquid-Phase Adsorption: A Mini-Review. Chem. Eng. J. 2009, 151, 1–9. 10.1016/j.cej.2009.02.024. [DOI] [Google Scholar]
  83. Quek S. Y.; Al-Duri B. Application of Film-Pore Diffusion Model for the Adsorption of Metal Ions on Coir in a Fixed-Bed Column. Chem. Eng. Process. Process Intensif. 2007, 46, 477–485. 10.1016/j.cep.2006.06.019. [DOI] [Google Scholar]
  84. Sekine T.; Nakatani K. Intraparticle Diffusion and Adsorption Isotherm for Sorption in Silica Gel Studied by Single-Microparticle Injection and Microabsorption Methods. Langmuir 2002, 18, 694–697. 10.1021/la0110500. [DOI] [Google Scholar]
  85. Robati D. Pseudo-Second-Order Kinetic Equations for Modeling Adsorption Systems for Removal of Lead Ions Using Multi-Walled Carbon Nanotube. J. Nanostructure Chem. 2013, 3, 55. 10.1186/2193-8865-3-55. [DOI] [Google Scholar]
  86. Peers A. Elovich Adsorption Kinetics and the Heterogeneous Surface. J. Catal. 1965, 4, 499–503. 10.1016/0021-9517(65)90054-0. [DOI] [Google Scholar]
  87. Choy K.; Porter J.; McKay G. Film-Surface Diffusion during the Adsorption of Acid Dyes onto Activated Carbon. J. Chem. Technol. Biotechnol. 2004, 79, 1181–1188. 10.1002/jctb.1101. [DOI] [Google Scholar]
  88. Zhang H.; Chen L.; Lu M.; Li J.; Han L. A Novel Film-Pore-Surface Diffusion Model to Explain the Enhanced Enzyme Adsorption of Corn Stover Pretreated by Ultrafine Grinding. Biotechnol. Biofuels 2016, 9, 181. 10.1186/s13068-016-0602-2. [DOI] [PMC free article] [PubMed] [Google Scholar]

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