Dipaloy Datta

Herein, the catalytic reduction of 4-nitrophenol (4-NP) and the photocatalytic degradation of methylene blue (MB) dye using an easily synthesizable capsule-like A-ZnO-CuO (AZC) nanocomposite as an S-scheme heterojunction photocatalyst are reported. The properties of A-ZnO (AZ) and AZC nanocomposite samples were adjusted by the addition of the leaf extract of the Saraca asoca plant as a stabilizing and reducing agent. The nanocomposite was synthesized using an eco-friendly approach, ensuring sustainability and minimizing environmental impact. The formation of AZ and AZC nanocomposite samples was confirmed by different spectroscopic and microscopic techniques (UV-vis diffuse reflectance spectroscopy (DRS), field-emission scanning electron microscopy associated with energy-dispersive X-ray, Fourier transform infrared spectroscopy, high-resolution transmission electron microscopy, and X-ray diffraction). By plotting the DRS absorbance data in Tauc's equation, the bandgap energy of all of the as-prepared samples was investigated. Among all of the as-prepared samples, the capsule-like AZC3 nanocomposite material was found to show excellent photocatalytic activity in breaking down the MB dye up to 96.2% using a modest catalyst loading and 20 mg/L dye concentration that follows pseudo-first-order kinetics. Further, this novel nanocomposite is proven to be an effective catalyst in the reduction of 4-NP to 4-aminophenol using NaBH₄ as a reducing agent. The integration of CuO with ZnO facilitates enhanced electron transfer, thereby accelerating both the photocatalytic degradation of the MB dye and the catalytic reduction of 4-NP. Moreover, the catalyst exhibits exceptional stability over multiple cycles, demonstrating its potential for large-scale wastewater treatment applications. Additionally, the dual functionality of the catalyst in addressing multiple organic pollutants further enhances its feasibility for practical environmental remediation.

Almond resin (a natural polymer) was incorporated with an amine solvent (Aliquat-336) by wet impregnation method in an ultrasonicator. The surface morphology, functional groups, thermal stability, and surface area were determined. The point of zero-charge on the surface was also found out. The performance of the impregnated resin was analyzed by treating Bisphenol-A (BPA) and Biochanin-A (BA) containing aqueous solutions by varying experimental parameters such as dosage amount, contact time, temperature, initial concentrations of BPA and BA, and solution pH. Pseudo-second-order kinetic model and Freundlich isotherm rendered the best fit for BPA and BA adsorption data. A double layer thermodynamic adsorption model was applied to estimate the adsorption energy and positional entropy of the process.

The present work reports studies on the effective removal of Rhodamine-B (RhB) using Aliquat-336 modified Amberlite XAD-4 resin in the fixed-bed columns in series. The effect of flow rate (Q = 2 to 6 mL·min−1), bed height (h = 3.5 to 7 cm) and initial RhB dye concentration (Cin = 10 to 20 mg·L−1) was studied. When a single column was used, 93% RhB dye was removed in 3 h at Q= 2 mL·min−1, Cin = 10 mg·L−1, and h = 7 cm. When three columns in series were used, almost 100% dye was removed until 80 h. The maximum breakthrough time (142 h) and saturation time (244 h) were found by keeping Q= 2 mL·min−1, h = 7 cm of each column and Cin = 10 mg·L−1. Mathematical modeling of the breakthrough curves was done by using Yoon-Nelson, Clark, Wolborska, and pore diffusion models. The Clark model best fitted the experimental data. The possible interaction mechanism between Aliquat-336 and RhB dye was proposed. The column was regenerated in continuous mode using 1 M HCl solution and maintaining a flow rate of 2 mL·min−1.

Malachite green dye was removed using three different polymeric resins (Amberlite XAD7, Amberlite 120H and Amberlite IRA67). Equilibrium and kinetic experiments were carried out to determine the effect of contact time (0-120 min), resin dose (0.05-0.4 g), initial dye concentration (10-50 mg/L), temperature (303-323 K), pH (2-12) and NaCl concentration (0.5-50 g/L) on the adsorption capacity of all the resins. With an increase in the resin amount, a sharp decrease in the adsorption capacity was observed. The removal efficiency of dye was found to be 98.29% with IRA67, 99.27% with XAD7, and 98.66% with IR120H after 120 min. Temkin isotherm matched equilibrium data for XAD7 and IR120H, whereas Freundlich isotherm model best described the results for IRA67, pH, temperature and NaCl did not affect the removal efficiency significantly. Kinetic data were well fitted with pseudo-second order rate kinetics. All the three resins were regenerated using 1 M NaOH solution showing good reusability.

Reactive dyes are highly soluble in water, and carcinogenic. Therefore, it is essential to remove these dyes from their aqueous solutions. This study focused on the simultaneous removal of reactive orange 16 (RO) and reactive green 19 (RG) dyes from their binary dye solution using Cyphos IL101-impregnated Amberlite XAD7HP resin (ILX7) in batch and recirculating stirrer vessel (RSV). In the batch study, the experimental operating conditions were designed by using central composite design of response surface methodology. Influence of important input variables (RO dye concentration, RG dye concentration, pH, and resin dosage) on the dye adsorption was studied and their values were optimized. At the optimum values of input variables, equilibrium, kinetic, and thermodynamic studies were performed for the binary dye mixture. The equilibrium and kinetic adsorption data were best fitted with extended-Freundlich and pseudo-second-order models, respectively. Now to intensify the process, continuous studies were performed in a RSV at optimum conditions and at different flow rates and stirring speeds. The impregnated resin was regenerated by using 80% v/v ethanol and successfully reused up to 3 cycles with slight decrease in the adsorption capacity. Graphical abstract

In the present study, thionine dye was adsorbed on the surface of the peanut hull. Experiments were carried out by changing speed of agitation (50–300) rpm, time of contact (0–300) min, initial concentration of dye (10–50 mg/L), adsorbent dose (2–8 g/L), solution pH (2–12), and temperature (298–333 K) to evaluate their effect on the adsorption. The characterisation of the peanut hull was done by using XRF, FTIR and SEM. The optimum conditions were found as agitation speed = 200 rpm; time of contact = 300 min; initial dye concentration = 20 mg/L; adsorbent dose = 4 g/L; solution pH = 8 and temperature = 313 K. Equilibrium isotherm and kinetic models were studied to estimate their parameters and to predict adsorption capacity of peanut hull. Langmuir isotherm was found to be the best-fitted isotherm with R ² of 0.992 and contributes the maximum adsorption capacity of 8.45 mg/g. Pseudo-first-order describes the kinetics with R ² equal to 0.99. The change in enthalpy and entropy were also estimated from Gibbs’ free energy.