Skip to main content
NCBI home page
ACS Omega logoLink to ACS Omega
. 2020 Jul 28;5(31):19548–19556. doi: 10.1021/acsomega.0c02011

Dewaxed Honeycomb as an Economic and Sustainable Scavenger for Malachite Green from Water

Roshni Kumari †, Md Adnan Khan †, Mithilesh Mahto †, Md Atif Qaiyum †, Jhilirani Mohanta †, Banashree Dey ‡, Soumen Dey †,*
PMCID: PMC7424748  PMID: 32803049

Abstract

graphic file with name ao0c02011_0008.jpg

Dewaxed honeycomb powder (HCP) was used as a promising adsorbent for removal of malachite green (MG) from aqueous solution. Raw honeycomb was strategically dewaxed by petroleum ether, and the purified product was characterized by Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), pHzpc, and proximate analysis. A high uptake capacity (123 mg/g) was found at neutral pH. Experimental data follow pseudo-second-order kinetics (k2 as 0.45 × 10–2 g/min/mg, R2 = 0.986) and Langmuir isotherm with R2 0.999. Thermodynamic parameters suggested a spontaneous (ΔG = −26.28 kJ/mol) and exothermic (ΔH = −11.61 kJ/mol) process, which suggests increased randomness (ΔS = 0.0486 kJ/mol) at the solid–liquid interface during the adsorption process. The material can be regenerated by ordinary salt solution (1 M NaCl) and efficiently reused for three cycles with a minimal loss in efficiency. Adsorption mechanism is proposed to be a combination of electrostatic interaction and π–π stacking between aromatic units of HCP and MG. Abundant availability, possibility of wax commercialization, economic sustainability, and comprehensive waste management make HCP an ideal choice for dye decolorization.

1. Introduction

Dyes are used as colorants in a large number of industries such as paper, pharmaceutical, textile, leather, printing, rubber, food processing, etc. Dye-containing industrial effluent is the chief source of water pollution and poses a serious threat to the aquatic environment. Dyes are highly stable complex organic molecules that are nonbiodegradable, carcinogenic, and mutagenic. Dyes reduce light penetration and decrease the gross productivity of flora and fauna. Malachite green (MG) is a cationic dye widely used as a coloring agent and disinfectant. Its discharge into water bodies creates threat to humans and the environment.1 Many researchers explored different techniques for removal of dyes from water. Physical methods like ion exchange, ozonation, membrane separation, coagulation, and adsorption are mostly studied.2 Among all, adsorption stands as the most effective method because of simple design, easy implementation, eco-friendliness, nontoxicity, sustainability, and economic feasibility.3 Adsorption on activated carbon was being practiced worldwide. However, due to its high cost and poor regeneration capacity, researchers are now focusing on alternative natural adsorbents. The use of natural adsorbents has several advantages like high cost-effectiveness, biodegradability, and nontoxicity. These include Citrus limetta peel, pomegranate peel, Luffa sponge, breadnut peel, Thuja orientalis leaves, Walnut shell powder, aloevera leaves, oat hull, tobbaco stem biomass, coconut shell powder, pomelo peels, raw and modified rice husk, oil palm tree sawdust, leaf-based adsorbents, and so on.4−18 Moreover, use of such agricultural and nonagricultural waste provides a sustainable and efficient platform for wastewater treatment. This leads to the development of a new and innovative material that satisfies the current scenario of treatment techniques. However, most of the available materials do not open up any new window apart from treatment options.

Previously, we have reported the use of Eucalyptus leaves (Eucalyptus globulus) and coco-peat (Cocos nucifera) for dye removal from aqueous environment.19,20 In line with this, we herein report the use of waste honeycomb as a potential adsorbent for the removal of malachite green. Different types of honeycombs are abundantly available in most part of the world. Honeycombs, after extraction of honey, are left isolated and abandoned. Eventually, they fall down and become a waste. Such waste honeycomb consists of wax, sugars, acids, esters, and polyphenolic compounds like flavonoids that can provide a reactive surface for interaction with dye molecules.21 The present work reports the potential of honeycomb waste as an efficient adsorbent for removal of malachite green as a sustainable alternative. This work is aimed to meet the following objectives: (i) preparation of wax-free honeycomb powder (HCP), a new promising adsorbent for MG removal in batch test, (ii) kinetics and isotherm modeling along with thermodynamic insights to better understand adsorption mechanisms, (iii) regeneration study and cyclewise efficiency, and (iv) cost–benefit analysis of the adsorbent for possible outcome in the society.

2. Results and Discussion

2.1. Characterization of HCP

HCP was characterized by pHZPC, Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy–energy-dispersive X-ray spectroscopy (SEM-EDS), and proximate analysis. Zero point charge was estimated by the pH drift method to be 5.5 (Figure 1a). The isoelectric point or the zero point charge of an adsorbent plays a crucial role in determining the adsorption property of a material with respect to a specific adsorbate as it defines the particular pH at which the surface of the material is neutral or the net charge on the surface is zero. At pH < pHZPC, the surface of the material is positive; at pH > pHZPC, the surface is negative; and at pH = pHZPC, the surface is neutral.22,23 This suggests that the surface of HCP becomes negative beyond pH 5.5, indicating the favorable adsorption of a cationic dye at higher pH.

Figure 1.

Figure 1

Open in a new tab

(a) ZPC of HCP. (b) FTIR spectra of HCP before and after adsorption.

The presence of functional groups was evaluated by the FTIR spectrum (Figure 1b). The peak at 3280 cm–1 is related to phenolic O–H stretching. The peaks at 2915 and 2848 cm–1 represent aromatic and aliphatic C–H stretching, the peak at 1525 cm–1 corresponds to O–H bending, and the peak at 1028 cm–1 may be attributed to C–N stretching. The bands at 1629 and 1525 cm–1 may be assigned to C=O stretching and O–H bending vibrations, respectively.24,25 Weak absorption peaks from 1150 to 1450 cm–1 were assigned to C–O bending vibrations. After adsorption, the peaks corresponding to 3280, 2915, 2848, 1379, and 1028 cm –1 were found to shift to 3224, 2910, 2778, 1370, and 1032 cm–1, respectively. Such observations clearly signify the successful bonding of MG with the functional moieties on HCP. Phenolic −OH undergoes hydrogen bonding with dye molecules, resulting in a decrease of bond stretching from 3280 to 3224 cm–1. Such lowering is due to weakening of the −OH bond. The above observation also recommends the formation of possible π–π stacking interaction (aromatic C–H shift) along with hydrogen-bonding (O–H shift) interactions.

Since the composition of a waste biomass cannot be exactly known, an important tool for physical characterization is proximate analysis which gives an idea about fixed carbon, ash, volatile matter, and moisture content of the material. Proximate analysis was done by heating the sample (0.2 g for each set) at different temperatures (250, 350, and 500 °C) for different time periods (40, 15, and 3 min respectively) to estimate moisture, ash, and volatile matter of the material, respectively. Actual carbon content was calculated by subtracting the sum of these three from 100. Fixed carbon content (35.5%) represents the organic moieties present in the adsorbent that are involved in the adsorption process. The amount of ash obtained (38%) can be used as another biomaterial in its native form itself or with suitable activation. Volatile matter component is a rough measure of the porosity. In this case, it was found to be 2.1%. Such a low content is matched with SEM images. Moisture content (24.4%) parallels the polarity of surface due to the high dielectric constant of water. The result of relevant parameters is illustrated in Table 1.

Table 1. Selected Parameters of Proximate Analysis.

content percent
moisture 24.4
ash 38.0
volatile matter 2.1
fixed carbon 35.5
Open in a new tab

SEM-EDS are useful to determine the surface microstructure, texture, morphology, and composition of HCP. SEM micrographs are presented in Figure 2a,b. Morphological images show a rough, uneven surface with occasional pits and fracture. A few channels could also be identified. After the adsorption surface becomes compact, evenly dispersed and looks saturated with dye molecules. Channels are less visible after adsorption. EDS gives the elemental composition of the material before and after adsorption. The resultant peaks are presented in Figure 2c,d. Changes in peak appearance confirm successful dye adsorption. MG contains nitrogen as one of the components, which appears as a strong peak after adsorption.

Figure 2.

Figure 2

Open in a new tab

SEM morphology of HCP: (a) before adsorption and (b) after adsorption. SEM-EDS (c) before adsorption and (d) after adsorption.

2.2. Effect of Contact Time

Contact time is an important parameter for the determination of equilibration point. Figure 3a presents the adsorption profile with respect to time. The adsorption percentage increases from 68 to 92% upon increasing time from 20 to 100 min, respectively. After that, a nominal increase (92–96%) was noted for the time interval of 100–120 min. It could be seen that adsorption (both percentage and uptake capacity) is initially rapid due to the availability of a larger number of vacant sites at the adsorbent surface and gradually slows down due to the decreasing number of empty sites on the surface. After 100 min, the repulsive and competitive inhibition between the adsorbed dye molecules and the approaching dye molecules increases till saturation of the vacant sites. Such an effect is responsible for the slow increase in adsorption percentage and uptake capacity. After 120 min, complete saturation of the active sites occurs. Thus, 120 min was chosen as optimum batch test time for all experiments.

Figure 3.

Figure 3

Open in a new tab

Effects of (a) contact time, (b) initial concentration, (c) pH, and (d) pH on uptake capacity.

2.3. Effect of Initial Concentration

Adsorption was found to increase from 57 to 82% with an increase in dye concentration (10–80 mg/L), as shown in Figure 3b. This is due to the increased driving force offered by the adsorbed dye molecules, which facilitates the transfer of dye molecules at the adsorbent–adsorbate interfaces.23 An increase in the initial concentration of the dye increases the collisions between the dye molecules and the adsorbent surface, thereby increasing the adsorption percentage. Further, the cumulative driving force offered by the adsorbed dye molecules also helps free dye molecules to overcome the mass flow resistance to approach the active sites. Eventually, such phenomena finally lead to their attachment on the active sites. This driving force increases with an increase in adsorbate concentration and results in an increased adsorption percentage with increasing concentration.22

2.4. Effect of pH

Solution pH plays a key role in determining the nature of adsorption and the mechanism involved. HCP consists of various functional moieties like carboxylic acid, hydroxyl, phenolic −OH, etc. Such groups are influenced by acidic or alkaline medium.22 Adsorption profile with varying pH is shown in Figure 3c,d; 68–70% adsorption was seen in the low pH range (3–5), while a rapid increase was noted above pH 5.5. Such an increase (70–96%) is attributed to the change in the surface charge of HCP (pHZPC = 5.5). At pH > pHZPC, the surface is negative, which favors the adsorption of cationic dye. The electrostatic interaction between positively charged MG and negatively charged surface of HCP facilitates adsorption. At pH < pHZpc, the surface of HCP is positively charged, so the removal efficiency is low due to the electrostatic repulsion between MG and protonated HCP. Additional competitive forces from abundant H+ ions also influence the system. The adsorption proceeds through hydrogen bonding predominantly. Similar observations were seen earlier.26 Above pH 8, adsorption was found to become constant. Moreover, MG is known to change its color at alkaline pH (>8). MG solution used for experiment shows pH 6.8 under ambient conditions. Since we obtained a good adsorption percentage (91%) automatically, pH 6.8 was fixed for other experiments.

2.5. Adsorption Kinetics

Kinetics was analyzed using three models, namely, pseudo-first-order, pseudo-second-order, and intraparticle diffusion models. Rate constants were evaluated from the following rate equations (eqs 1, 2, and 3)

Pseudo-first order:

2.5. 1

Pseudo-second order:

2.5. 2

where qt and qe represent the amount (mg/g) of dye adsorbed at time t and at equilibrium, respectively. The slope of the plot of log (qe – qt) vs t gives the pseudo-first-order rate constant k1. The intercept of the plot of t/qt vs time helps to determine the pseudo-second-order rate constant k2.

The intraparticle diffusion model is expressed as

2.5. 3

where kid is the intraparticle rate constant, determined from the slope of the qt vs t1/2 plot, and C is the intercept that represents the boundary layer thickness. The values of different kinetic rate constants along with their R2 are illustrated in Table 2.

Table 2. Selected Kinetic Parameters.

kinetic model parameters value
pseudo-first-order qe (mg/g) 9.16
k1 2.12 × 102 (1/min)
R2 0.854
pseudo-second-order qe (mg/g) 36.80
k2 0.45 × 10–2 (g/mg/min)
R2 0.986
intraparticle diffusion qe (mg/g) 21.40
kid 0.21 (mg/g·min1/2)
R2 0.806
Open in a new tab

The pseudo-first-order model assumes that the rate of adsorption depends on the available number of active empty sites on the adsorption surface.27,28 The pseudo-first-order plot is shown in Figure 4a. The pseudo-second-order model depends on both the number of vacant sites on the adsorbent surface and the number of occupied sites on the adsorbent surface. The pseudo-second-order plot was found to have best fit with R2 = 0.986 (Figure 4b).29 This suggests that the rate is governed by the electrostatic forces through sharing of oppositely charged surfaces in adsorbent–adsorbate systems.

Figure 4.

Figure 4

Open in a new tab

(a) Pseudo-first-order plot, (b) pseudo-second-order plot, and (c) intraparticle diffusion plot.

Intraparticle diffusion suggests that mass transfer of the MG dye is mediated by a diffusion-controlled process. The actual mass transfer mechanism between the solid and bulk phases is governed by three steps. Dye molecules transfer through a diffusive pathway to the adsorbent surface across the external liquid layer. Then, attachment of the dye molecules at the vacant active sites on the adsorbent takes place. This is followed by pore diffusion. In addition, the curve of the intraparticle plot seems not to pass through the origin, suggesting that the diffusive mass transfer was not the rate-limiting step. A similar observation was found with other systems.28,30,37,38Figure 4c presents the intraparticle diffusion plot.

2.6. Adsorption Isotherm

Isotherm study describes the distribution of adsorbate in solution and the amount adsorbed on a particular adsorbent at a specific temperature. Two isotherm models, namely, Langmuir and Freundlich, were tested.

The Langmuir model describes a monolayer adsorption on a homogeneous, uniform surface of adsorbent.26 Binding of a dye molecule at a specific site is independent of the adjacent site. The site can be occupied only once, and a dynamic adsorption mechanism follows at the rate of adsorption–desorption.31 The Langmuir model can be presented by the following equation (eq 4)

2.6. 4

where qe is the amount of dye adsorbed per unit adsorbent (mg/g), Ce is the concentration of the solution at equilibrium (mg/L), Qm is the maximum adsorption capacity (mg/g), and b is the Langmuir rate constant (L/mg). The plot of Ce/qe vs Ce is presented in Figure 5a. The values of Qm and b were estimated from the corresponding slope and intercept. The Langmuir model is better interpreted by a dimensionless parameter known as the separation factor (RL) (eq 5)

2.6. 5

where C0 is the initial concentration of the dye and b is the Langmuir constant. The feasibility and favorability could be explained with the help of RL. For 0 < RL < 1, adsorption is favorable. The value of RL was calculated to be 0.408, which suggests a favorable adsorption.

Figure 5.

Figure 5

Open in a new tab

(a) Langmuir plot and (b) Freundlich plot.

The Freundlich model is based on the assumption that there exists a multilayer adsorption of adsorbate molecules on the heterogeneous surface of adsorbent. It is expressed by eq 6

2.6. 6

where KF is the Freundlich constant related to capacity and 1/n is related to adsorption intensity, which depends on the heterogeneity of the biomaterial.28 The Freundlich model and selected parameters are presented in Figure 5b and Table 3.

Table 3. Selected Isotherm Constants.

  Langmuir
 Freundlich
temperature (K) Qm (mg/g) b (L/mg) R2 n KF (L/mg) R2
291 86.956 0.034 0.999 1.202 3.232 0.987
298 91.428 0.052 0.996 1.277 3.962 0.983
305 95.555 0.090 0.991 1.396 5.321 0.981
Open in a new tab

The results showed that adsorption follows the Langmuir isotherm with R2 =0.991 and adsorption capacity of 95.555 mg/g. This result indicates that the monolayer adsorption is assisted by a uniform distribution of dye molecules onto the HCP surface. In addition, constant b was found to increase with increasing temperature, which suggests that enhanced adsorption takes place with increasing temperature. Such observation is also supported by the increasing Gibb’s free energy. From Freundlich data, it was seen that the value of n is greater than unity. Such values along with high correlation coefficients suggest that the involvement of multilayer adsorption cannot be ruled out.

2.7. Adsorption Thermodynamics

Thermodynamic parameters deal with the energy changes involved in an adsorption process. Relevant equations are given below (eqs 7 and 8).

2.7. 7
2.7. 8

where Kc denotes the rate constant which corresponds to the equilibrium concentration of solute on adsorbent to the equilibrium concentration of solute in solution, R represents the universal gas constant (8.314 J/mol/K), T represents the temperature (K), ΔG represents the Gibbs free-energy change, which determines spontaneity of a process, and ΔH and ΔS represent the enthalpy and entropy changes, respectively. The plot of ln Kc vs 1/T gives a straight line, from which ΔH0 and ΔS0 were obtained from the corresponding slope and intercept values. Selected thermodynamic parameters are illustrated in Table 4. Negative values of ΔG (−25.94 to −30.06 kJ/mol) suggest a spontaneous process. Negative ΔH indicates an exothermic reaction, and the present values (−11.61 to −16.89 kJ/mol) reveal that the adsorption proceeds through physisorption (ΔH < 20 kJ/mol).32 The values of ΔH between 20.9 and 418.4 kJ/mol signify chemisorption, as reported in the biosorption of cadmium by cyanobacterium biomass (ΔH = −41.85 to −49.16 kJ/mol).32 Positive ΔS suggests a slight increase in randomness at the adsorbate–adsorbent interface. The increasing ΔS (0.0486–0.0599 kJ/mol) with temperature specifies an increase in affinity of the adsorbate toward the adsorbent surface, which is supported by the enhanced free-energy changes with temperature. Contrary to this, negative ΔS suggests decreased randomness at the solid–solution interface during the adsorption process, as reported for the biosorption of cadmium by cyanobacterium biomass (ΔS = −0.102 to −0.126 kJ/mol).32 The relevant van’t Hoff plot is shown in Figure 6a.

Table 4. Selected Thermodynamic Parameters.

concentration (mg/L) temperature (K) ΔG (kJ/mol) ΔH (kJ/mol) ΔS (kJ/mol)
10 291 –25.94 –11.61 0.0486
298 –26.28 –11.61 0.0486
305 –26.62 –11.61 0.0486
30 291 –29.23 –16.89 0.0599
298 –29.65 –16.89 0.0599
305 –30.06 –16.89 0.0599
Open in a new tab

Figure 6.

Figure 6

Open in a new tab

(a) van’t Hoff plot and (b) Arrhenius plot.

2.8. Activation Energy

The activation energy of the process was calculated by the Arrhenius equation (eq 9).

2.8. 9

where A, Ea, T, and R represent the temperature-independent factor (g/mg/min), activation energy (kJ/mol), temperature (K), and universal gas constant (8.314 J/mol/K), respectively. By plotting ln Ka vs 1/T, Ea was evaluated (Figure 6b). The activation energy (Ea) was found to be 20.124 and 17.218 kJ/mol for two concentrations, i.e., 10 and 30 mg/L, respectively. Activation energy in the range of 5–20 kJ/mol represents physisorption, and that in the range of 20–400 kJ/mol represents chemisorption.33 It is proposed that the process is between physisorption and chemisorption. Earlier we have shown the range of activation energies in different dye–adsorbent systems.34−36 The results of thermodynamic analysis as well as the activation energy data together suggest that adsorption proceeded through physisorption predominantly, which is underlined by the adherence of the adsorbate molecules to the solid (adsorbent) surface by van der Waals forces or other weak intermolecular forces. Hence, the adsorption mechanism is proposed to be a combination of various forces including electrostatic attraction, hydrogen bonding, and π–π interaction. A brief discussion on this is given in the Supporting Information. Figure S1 represents the possible schematic binding mechanism.1,19

2.9. Regeneration and Reuse

Regeneration is important to ascertain reusability of exhausted material. Regenerations of 78, 6, and 3% were achieved with 1 M NaCl, 1 M HCl, and 1 M NaOH, respectively. It is proposed that there are some ion-exchange interactions between the dye molecule and sodium ion. Upon successful regeneration, HCP was tested for reusability. It was found that up to three cycles, the material shows good efficiency with 1 M NaCl. Regeneration and cyclewise efficiency are presented in Figure 7a,b, respectively.

Figure 7.

Figure 7

Open in a new tab

(a) Regeneration of HCP and (b) cyclewise efficiency of HCP.

2.10. Comparison of Uptake Capacities of Few Adsorbents for MG

A new material can be considered promising if it shows some advantage over the existing ones. Hence, the maximum uptake capacity of MG by HCP is compared to other reported biomass. Peroxide-treated rice husk and NaOH-modified rice husk were reported for MG removal with uptake capacities of 26.6 and 15.50 mg/g, respectively.15,17 Pomegranate peel shows a capacity of 31.45 mg/g.9 Thus, the comparative study suggests a better sorption performance of HCP than many others. Hence, it can be concluded that HCP is a promising scavenger for MG. Uptake capacities of different adsorbents are illustrated in Table 5.

Table 5. Comparison of Uptake Capacities of Various Adsorbents for MG.

sl. no. adsorbent uptake capacity (mg/g) reference
1 coconut shell powder 214.63 (13)
2 pomelo peels 178.43 (14)
3 breadnut peel 353 (10)
4 modified rice husk 26.6 (15)
5 oil palm tree sawdust 65.36 (16)
6 pomegranate peel 31.45 (9)
7 NaOH-modified rice husk 15.50 (17)
8 C. limetta peel 8.73 (7)
9 oat hull 83 (5)
10 lotus leaf 113.8 (37)
11 Carica papaya wood 52.63 (38)
12 Melaleuca diosmifolia 116.28 (39)
13 HCP 123 this study
Open in a new tab

2.11. Economic Aspect of HCP

Since honeycomb is a material found in various parts of the globe, it could be an ideal choice in terms of free availability. A successful technoeconomic approach is essential to earmark a material as a potential and sustainable one. For making 40 g of HCP, 125 g of raw material and 600 mL of petroleum ether were used. Petroleum ether of volume 500 mL costs approximately INR 215 only (∼USD 3). From 125 g of raw material, about 80 g of wax was isolated, which has a market price of INR 115 only (∼USD 1.5). Equivalently, 40 g of HCP production costs INR 110 (USD 1.5). It is noteworthy that, upon large-scale extraction (>500 g), cost gets reduced by half. Thus, this method is a revenue-generating one. Moreover, production can be scaled up to any extent. We have achieved dye detoxification, waste management, and revenue generation simultaneously. In addition, recycled petroleum ether can be used for next-step HCP preparation and glue removal from a surface. This enables a high output/input ratio. To summarize, the process partially meets the requirement of green engineering. We have also scaled up the wax recovery from raw HC and found that about 71–73% (71–73 g out of 100 g raw material) wax recovery is possible. Wax recoveries in the second and third cycles were about 97 and 93% of that of the first cycle, respectively. Hence, it can be concluded that HCP is an ideal choice for a sustainable water treatment.

3. Conclusions

Abundantly available honeycomb was chosen as a potential scavenger in wastewater treatment. Efficient removal of malachite green from aqueous solutions by dewaxed honeycomb powder was established. Dewaxed honeycomb was characterized by FTIR, SEM, proximate analysis, and pHZPC. High adsorption capacity of up to 123 mg/g was obtained at ambient pH. The adsorption process follows the Langmuir isotherm and pseudo-second-order kinetics. Thermodynamic data confirm that the process is spontaneous, feasible, and exothermic in nature. Regeneration of up to 78% was achieved with sodium chloride solution, and the remarkable reusability of the material makes it a sustainable one. Easy regeneration of HCP is particularly advantageous. A good quantity of wax was isolated from the process, which boosts the advantage of the protocol. Cost–benefit analysis strongly advocates the suitability and sustainability of the material for wastewater treatment.

4. Experimental Section

4.1. Materials and Methods

4.1.1. Chemicals and Reagents

A.R.-grade petroleum ether, hydrochloric acid, sodium hydroxide, sodium chloride, and acetone were purchased from Rankem Chemicals (Mumbai, India). Malachite green (MG) dye was purchased from Merck. Millipore water was used to make all solutions.

4.2. Instrumentation

A rotary orbital shaker incubator (Sohag, India) was used for mechanical shaking. A muffle furnace (Thermo Scientific, Philippines) and a digital pH meter (Systronics, India) were used for drying and pH measurements, respectively. A PerkinElmer spectrum-II and a Hitachi double-beam UV–Vis spectrophotometer (model U-2900, Japan) equipped with UV solutions program were used for FTIR analysis and colorimetric measurements, respectively. A ZEISS SEM analyzer (Germany) and a benchtop centrifuge, R-8 M (Remi, Kolkata, India), were used for SEM analysis and centrifugation, respectively.

4.3. Preparation of Dye Solution

A stock solution of malachite green (500 mg/L) was prepared by dissolving 0.05 g of dye in 1000 mL of distilled water. Required dilutions were made for various experiments. The absorbance was recorded at 618 nm (λmax) using a UV–visible spectrophotometer, and the corresponding concentrations were obtained using a prestandardized calibration curve.

4.4. Collection and Treatment of Honeycomb

Honey bees (Apis mellifera) deposit honey inside beehives. After removal of honey, the honey-free combs are set free. Eventually, they get ruptured and fall down with time. Fallen honeycombs (HCs) were collected from our university campus in the months of September–October. The raw material was washed thoroughly with water to remove adhering dirt and then refluxed in water to remove soluble sugar components. The mixture was filtered and subjected to oven drying at 80 °C for 48 h. The light brown material was then cut into small pieces (approximate dimension: 0.5 cm × 0.8 cm × 0.2 cm) and twice refluxed in petroleum ether for 2 h and filtered hot. The treated honeycomb was then washed with ethanol and dried at 80 °C overnight. The dewaxed honeycomb was ground by a mixer grinder (BAJAJ NEO JX 4 juicer mixer grinder, India) and sieved (Genware stainless steel flour sieve, India) to obtain the desired particle size (0.049 cm). Meanwhile, hot petroleum ether containing wax was rapidly cooled so that the wax gets deposited and vaporization loss of petroleum ether is nullified. A careful separation of petroleum ether yields pure wax. The schematic preparation of HCP is shown in Scheme S1 (Supporting Information).

4.5. Batch Studies

Batch tests were conducted in 100 mL poly(tetrafluoroethylene) (PTFE) bottles. Typically, to each set, 0.1 g of the adsorbent was added in 50 mL of dye (50 mg/L) solution. The solution pH was 6.8 (without adjustment). It was kept as such to observe activity without any modification. For the study of contact time, dye solution (50 mg/L) and adsorbent (0.1 g) were kept in a thermostatic orbital shaker at 100 ± 5 rpm at room temperature. The bottles were taken out at regular intervals of 20 min for a total of 180 min followed by centrifugation at 4000 rpm for 5 min. Absorbance of all solutions was recorded, which gives the corresponding concentration of the dye using the standard calibration curve of MG (λmax = 618 nm). Concentration variation (10–80 mg/L) was tested keeping all other parameters constant. The effect of pH was tested in the range of 3–8. The solution pH was adjusted using NaOH (0.01 M) and HCl (0.01 M) solutions for this experiment. The used range of dyes would help to better predict the efficiency of the material for MG under different working conditions. For the estimation of maximum uptake capacity, MG (50 mL, 1000 mg/L, 6.8) was shaken with 0.4 g of HCP for 3 h. For kinetics, solutions were withdrawn at an interval of 20 min (significant changes in absorbance are seen after this interval) for a total observation time of 120 min (equilibration time). For isotherm study, temperatures of 291, 298, and 305 K were chosen. Adsorption is a surface phenomenon supported by weak forces; therefore, isotherm study was done with a step size of 7 K at 291, 298, and 305 K. Percentage adsorption and uptake capacity were calculated using eqs 10 and 11, respectively.

4.5. 10
4.5. 11

where C0 and Ce are the initial and final dye concentrations (mg/L), respectively, Ct is the dye concentration at equilibrium (mg/L), V is the volume of solution (L), and m is the mass of biosorbent (g).

4.6. Desorption Test

For desorption test, dye-saturated HCP was treated with acidic, basic, and neutral solutions (HCl, NaOH, and NaCl, respectively). To each set, 0.2 g of exhausted HCP was stirred overnight with three solutions (20 mL, 0.1 M) separately. Desorption percentage was calculated using the following equation (eq 12)

4.6. 12

where qde and qad are the desorbed and adsorbed amounts of dye, respectively.

Acknowledgments

R.K., M.A.Q., and J.M. acknowledge Central University of Jharkhand for fellowship.

Supporting Information Available

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsomega.0c02011.

  • Scheme of HCP preparation and adsorption experiments (Scheme S1) and mechanism of adsorption (Figure S1) (PDF)

The authors declare no competing financial interest.

Supplementary Material

ao0c02011_si_001.pdf (431.7KB, pdf)

References

  1. Khaniabadi Y. O.; Mohammadi M. J.; et al. Removal of Congo red dye from aqueous solutions by a low-cost adsorbent: Activated carbon prepared from aloe vera leaves shell. Environ. Health Eng. Manage. 2017, 4, 29–35. 10.15171/EHEM.2017.05. [DOI] [Google Scholar]
  2. Liu M.; Li X.; Du Y.; Han R. Adsorption of methyl blue from solution using walnut shell and reuse in a secondary adsorption for Congo red. Bioresour. Technol. Rep. 2019, 5, 238–242. 10.1016/j.biteb.2018.11.006. [DOI] [Google Scholar]
  3. Reffas A.; Bouguettoucha A.; Chebli D.; Amrane A. Adsorption of ethyl violet dye in aqueous solution by forest wastes, wild carob. Desalin. Water Treat. 2016, 57, 9859–9870. 10.1080/19443994.2015.1031707. [DOI] [Google Scholar]
  4. Khaniabadi Y. O.; Heydari R.; Nourmoradi H.; Basiri H.; Basiri H. Low cost sorbent for the removal of aniline and methyl orange from liquid-phase: Aloevera leaves wastes. J. Taiwan Inst. Chem. Eng. 2016, 68, 90–98. 10.1016/j.jtice.2016.09.025. [DOI] [Google Scholar]
  5. Banerjee S.; Sharma C. G.; Gautam R. K.; Chattopadhyaya M. C.; Upadhyay S. N.; Sharma Y. C. Removal of Malachite green, a hazardous dye from aqueous solutions using Avena sativa (oat) hull as a potential adsorbent. J. Mol. Liq. 2016, 213, 162–172. 10.1016/j.molliq.2015.11.011. [DOI] [Google Scholar]
  6. Reddy D. D.; Ghosh R. K.; Bindu J. P.; Mahadevaswamy M.; Murthy T. Removal of methylene blue from aqueous system using tobacco stems biomass: kinetics, mechanism, and single-stage adsorber design. Environ. Prog. Sustainable Energy 2017, 36, 1005–1012. 10.1002/ep.12542. [DOI] [Google Scholar]
  7. Singh H.; Chauhan G.; Jain A. K.; Sharma S. Adsorptive potential of agricultural wastes for removal of dyes from aqueous solutions. J. Environ. Chem. Eng. 2017, 5, 122–135. 10.1016/j.jece.2016.11.030. [DOI] [Google Scholar]
  8. Xu F.; Qi X. Y.; Kong Q.; Shu L.; Miao M. S.; Xu S.; Du Y. D.; Wang Q.; Liu Q.; Ma S. S. Adsorption of sunset yellow by luffa sponge modified luffa and activated carbon from luffa sponge. Desalin. Water Treat. 2017, 96, 86–96. 10.5004/dwt.2017.20925. [DOI] [Google Scholar]
  9. Gündüz F.; Bahar B. Biosorption of malachite green from an aqueous solution using pomegranate peel: equilibrium modelling, kinetic and thermodynamic studies. J. Mol. Liq. 2017, 243, 790–798. 10.1016/j.molliq.2017.08.095. [DOI] [Google Scholar]
  10. Chieng H. I.; Lim L. B.; Priyantha N. Enhancing adsorption capacity of toxic malachite green dye through chemically modified breadnut peel: equilibrium, thermodynamics, kinetics and regeneration studies. Environ. Technol. 2015, 36, 86–97. 10.1080/09593330.2014.938124. [DOI] [PubMed] [Google Scholar]
  11. Arya M. C.; Bafila P. S.; Mishra D.; Negi K. Adsorptive removal of Remazol Brilliant Blue R dye from its aqueous solution by activated charcoal of Thuja orientalis leaves: an eco-friendly approach. SN Appl. Sci. 2020, 2, 265 10.1007/s42452-020-2063-2. [DOI] [Google Scholar]
  12. Miyah Y.; Lahrichi A.; Idrissi M.; Khalil A.; Zerrouq F. Adsorption of methylene blue dye from aqueous solutions onto walnut shells powder: Equilibrium and kinetic studies. Surf. Interfaces 2018, 11, 74–81. 10.1016/j.surfin.2018.03.006. [DOI] [Google Scholar]
  13. Bello O. S.; Ahmad M. A. Coconut (Cocos nucifera) shell based activated carbon for the removal of malachite green dye from aqueous solutions. Sep. Sci. Technol. 2012, 47, 903–912. 10.1080/01496395.2011.630335. [DOI] [Google Scholar]
  14. Bello O. S.; Ahmad M. A.; Semire B. Scavenging malachite green dye from aqueous solutions using pomelo (Citrus grandis) peels: kinetic, equilibrium and thermodynamic studies. Desalin. Water Treat. 2015, 56, 521–535. 10.1080/19443994.2014.940387. [DOI] [Google Scholar]
  15. Ramaraju B.; Reddy P. M. K.; Subrahmanyam C. Low cost adsorbents from agricultural waste for removal of dyes. Environ. Prog. Sustainable Energy 2013, 33, 38–46. 10.1002/ep.11742. [DOI] [Google Scholar]
  16. Low L. W.; Teng T. T.; Rafatullah M.; Morad N.; Azahari B. Adsorption studies of methylene blue and malachite green from aqueous solutions by pretreated lignocellulosic materials. Sep. Sci. Technol. 2013, 48, 1688–1698. 10.1080/01496395.2012.756912. [DOI] [Google Scholar]
  17. Chowdhury S.; Mishra R.; Saha P.; Kushwaha P. Adsorption thermodynamics, kinetics and isosteric heat of adsorption of malachite green onto chemically modified rice husk. Desalination 2011, 265, 159–168. 10.1016/j.desal.2010.07.047. [DOI] [Google Scholar]
  18. Bulgariu L.; Escudero L. B.; Bello O. S.; Iqbal M.; Nisar J.; Adegoke K. A.; Alakhras F.; Kornaros M.; Anastopoulos I. The utilisation of leaf-based adsorbents for dyes removal: A review. J. Mol. Liq. 2019, 276, 728–747. 10.1016/j.molliq.2018.12.001. [DOI] [Google Scholar]
  19. Kumari R.; Mohnata J.; Dey B.; Dey S. Eucalyptus Leaf Powder as an Efficient Scavenger for Congo Red from Water: Comprehensive Batch and Column Investigation. Sep. Sci. Technol. 2019, 1–13. 10.1080/01496395.2019.1670208. [DOI] [Google Scholar]
  20. Kumari R.; Dey S. A Breakthrough Column Study for Removal of Malachite Green Using Coco–Peat. Int. J. Phytorem. 2019, 21, 1263–1271. 10.1080/15226514.2019.1633252. [DOI] [PubMed] [Google Scholar]
  21. Bogdanov S.Beeswax: Production, Properties, Composition, Control. In Bee Product Science, Springer: New York, 2016; Vol. 17, pp 1–19. [Google Scholar]
  22. Mondal N. K.; Suman K. Potentiality of banana peel for removal of Congo red dye from aqueous solution: isotherm, kinetics and thermodynamics studies. Appl. Water Sci. 2018, 8, 157 10.1007/s13201-018-0811-x. [DOI] [Google Scholar]
  23. Roy T. K.; Mondal N. K. Biosorption of Congo red from aqueous solution onto burned root of Eichhornia crassipes biomass. Appl. Water Sci. 2017, 7, 1841–1854. 10.1007/s13201-015-0358-z. [DOI] [Google Scholar]
  24. Gapsari F.; Madurani K. A.; Simanjuntak F. M.; Andoco A.; Wijaya H.; Kurniawan F. Corrosion inhibition of honeycomb waste extracts for stainless steel in sulfuric acid solution. Materials 2019, 12, 2120 10.3390/ma12132120. [DOI] [PMC free article] [PubMed] [Google Scholar]
  25. Sewu D. D.; Boakye P.; Woo S. H. Highly efficient adsorption of cationic dye by biochar produced with Korean cabbage waste. Bioresour. Technol. 2017, 224, 206–213. 10.1016/j.biortech.2016.11.009. [DOI] [PubMed] [Google Scholar]
  26. Feng Y.; Zhou H.; Liu G.; Qiao J.; Wang J.; Lu H.; Yang L.; Wu Y. Methylene blue adsorption onto swede rape straw (Brassica napus) modified by tartaric acid: equilibrium, kinetic and adsorption mechanisms. Bioresour. Technol. 2012, 125, 138–144. 10.1016/j.biortech.2012.08.128. [DOI] [PubMed] [Google Scholar]
  27. Saha P. D.; Bhattacharya P.; Sinha K.; Chowdhury S. Biosorption of congo red and indigo carmine by nonviable biomass of a new dieztastrain isolated from the effluent of a textile industry. Desalin. Water Treat. 2013, 51, 5840–5847. 10.1080/19443994.2012.762589. [DOI] [Google Scholar]
  28. Mishra V.; Balomajumder C.; Agarwal V. K. Zn (II) ion biosorption onto surface of Eucalyptus leaf biomass: Isotherm, kinetic and mechanistic Modelling. Clean: Soil, Air, Water 2010, 38, 1062–1073. 10.1002/clen.201000030. [DOI] [Google Scholar]
  29. Wang H.; Yuan X.; Wu Z.; Wang L.; Peng X.; Leng L.; Zeng G. Removal of basic dye from aqueous solution using Cinnamoum camphora sawdust: kinetics, isotherms, thermodynamics and mass-transfer processes. Sep. Sci. Technol. 2014, 49, 2689–2699. 10.1080/01496395.2014.940590. [DOI] [Google Scholar]
  30. Manippady S. R.; Singh A.; Basavaraja B. M.; Samal A. K.; Srivastava S.; Saxena M. Iron-carbon hybrid magnetic nanosheets for adsorption-removal of organic dyes and 4-nitrophenol from aqueous solution. ACS Appl. Nano Mater. 2020, 3, 1571–1582. 10.1021/acsanm.9b02348. [DOI] [Google Scholar]
  31. Sundari D. S.; Kariman A.; Mansouri H. R.; Kariman F. The effectiveness of natural, low cost adsorbent for removal of methylene blue. Int. J. ChemTech Res. 2015, 7, 2763–2768. [Google Scholar]
  32. Satya A.; Harimawan A.; Haryani G. S.; Johir M. A. H.; Vigneswarn S.; Ngo H. H.; Setiadi T. Batch study of cadmium biosorption by carbon dioxide enriched Aphanothece sp. dried biomass. Water 2020, 12, 264 10.3390/w12010264. [DOI] [Google Scholar]
  33. Singha N. R.; Roy C.; Mahapatra M.; Dutta A.; Deb Roy J. S.; Mitra M.; Chattopadhyay P. K. Scalable Synthesis of Collagenic-Waste and Natural Rubber-Based Biocomposite for Removal of Hg(II) and Dyes: Approach for Cost- Friendly Waste Management. ACS Omega 2019, 4, 421–436. 10.1021/acsomega.8b02799. [DOI] [PMC free article] [PubMed] [Google Scholar]
  34. Mohanta J.; Dey B.; Dey S. Sucrose Triggered, Self-sustained Combustive Synthesis of Magnetic Nickel Oxide Nanoparticles and efficient Removal of Malachite Green from Water. ACS Omega 2020, 5, 16510–16520. 10.1021/acsomega.0c00999. [DOI] [PMC free article] [PubMed] [Google Scholar]
  35. Mohanta J.; Dey B.; Dey S. Magnetic Cobalt Oxide Nanoparticles: Sucrose Assisted Self Sustained Combustion Synthesis, Characterization and Efficient Removal of Malachite Green from Water. J. Chem. Eng. Data 2020, 65, 2819–2829. 10.1021/acs.jced.0c00131. [DOI] [Google Scholar]
  36. Mohanta J.; Dey B.; Dey S. Highly Porous Iron-Zirconium Binary Oxide for Efficient Removal of Congo Red from Water. Desalin. Water Treat. 2020, 189, 227–242. 10.5004/dwt.2020.25570. [DOI] [Google Scholar]
  37. Han X.; Yuan J.; Ma X. Adsorption of malachite green from aqueous solutios onto lotus leaf: equilibrium, kinetic, and thermodynamic studies. Desalin. Water Treat. 2014, 52, 5563–5574. 10.1080/19443994.2013.813102. [DOI] [Google Scholar]
  38. Rangabhashiyam S.; Lata S.; Balasubramanian P. Biosorption characteristics of methylene blue and malachite green from simulated wastewater onto Carica papaya wood biosorbent. Surf. Interfaces 2018, 10, 197–215. 10.1016/j.surfin.2017.09.011. [DOI] [Google Scholar]
  39. Kuppusamy S.; Naidu R.; et al. Potential of Melaleuca diosmifolia as a novel, non-conventional and low-cost coagulation adsorbent for removing both cationic and anionic dyes. J. Ind. Eng. Chem. 2016, 37, 198–207. 10.1016/j.jiec.2016.03.021. [DOI] [Google Scholar]

Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Supplementary Materials

ao0c02011_si_001.pdf (431.7KB, pdf)

Articles from ACS Omega are provided here courtesy of American Chemical Society

RESOURCES