Prof. Animes Kr. Golder
Professor
Key Research Areas :Photocatalytic water treatment and water-splitting | Nanoparticles for water purification and sensor development | Electro-and bio-remediation of heavy metals | Advanced oxidation processes | Physicochemical water treatment techniques
- Phone No: +91 361 258 2269
- Email: animes@iitg.ac.in
- Room No: 101
Research
Photocatalytic Degradation Processes
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Recently, pharmaceutical wastewater has emerged as a major global concern due to the unfettered discharge of pharmaceutically active compounds (PhACs) into the environment. Photocatalysis is a promising and eco-friendly technique that can mineralize PhACs using a suitable photocatalyst that is functional in visible light. Herein, bio-based metals (Pt, Au, and Ni) doping was tested for the functionalization of TiO2 using S. edule and waste pineapple peel vegetal extract and showed a reduced bandgap of 2.45 to 3.02 eV from 3.29 eV for bare TiO2 along with delayed h+/e- recombination and improved hydrophilicity. The developed photocatalysts exhibited excellent degradation of ciprofloxacin (85.5%), chloroquine (94.6%), and furazolidone (90.4%) drugs under visible light irradiation. In summary, the nature-inspired metal doping process presents a promising solution for remediating wastewater by enhancing the photocatalytic activity of native photocatalysts.
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Despite several advantages, recovering photocatalysts from slurry solutions after the degradation process is challenging and limits their large-scale utilization. Immobilizing photocatalysts on substrates can eliminate the need for their recovery. Herein, we developed a polymer/adhesive-free TiO2-coated glass substrate for the photocatalytic degradation of MB dye under visible light irradiation. Microscopic morphology analysis revealed a highly uniform and crack-free TiO2 coating with 1.5 mL of casting solution containing 15 g/L TiO2 and 15% (v/v) nitric acid. The optimized glass substrate exhibited the highest degradation of 97.09%, 98.14%, and 99.40% for 50, 100, and 200 mg/L MB dye, respectively, within 5, 10, and 30 minutes under visible light irradiation. Therefore, the TiO2-coated glass substrate provides valuable insights into eliminating the need for catalyst recovery across multiple cycles of photocatalytic degradation.
Photocatalysts Recovery
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The photocatalysts must be recovered for reuse to minimize the treatment cost and avoid secondary water pollution due to the presence of catalyst particles. Herein, we have studied the recovery of TiO2 and Pt-doped TiO2 (Pt/TiO2) photocatalysts using a pilot scale cross-flow ultrafiltration (CF-UF) membrane system with a nominal area of 2 m2 and pore size of 75 kDa. Pure water flux (PWF), permeate flux, and catalyst recovery (%) decreased with increased pH and catalyst concentration. The flux was reduced from 11.12±0.15 to 10.56±0.17 and 10.37±0.19 L m-2 h-1 during the recovery of TiO2 and Pt/TiO2 (50 mg L-1), respectively. The recovery of about 99.74±0.13 and 99.41±0.29% of TiO2 and Pt/TiO2 (50 mg L-1), respectively, was achieved at the optimized pH 5. Membrane fouling and flux recovery studies revealed excellent antifouling properties of the membrane with a maximum of 9.86±0.04% reversible fouling and a minimum of 98.78±0.20% flux recovery. The hydrodynamic diameters of both catalyst particles increased in the reject and backflush streams with right-tailed lognormal distribution.
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The recovery of photocatalysts after the photocatalytic degradation process is mandatory for its reuse. It is desired that the treated water be free from catalysts for consumption. However, the efficient recovery of photocatalysts is quite challenging. Although, magnetic catalysts have the advantage of easy recovery by applying a magnetic field. Herein, we have prepared a bio-based magnetic iron oxide (Fe3O4) catalyst using a vegetal extract of Mimosa pudica with an average particle size of 35 nm. The bio-based Fe3O4 exhibited a bandgap of 1.5 eV with saturation magnetization of 74 emu/g and found to be mesoporous with a surface area of 32.71 m2/g. The synthesized catalyst was employed for the photodegradation of ciprofloxacin (CIP) and exhibited 74% degradation under visible light within 120 min. After photodegradation, the magnetic field was applied and a complete recovery was observed within 10 min.
Electrochemical and Optical Sensing
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A large number of synthetic pesticides are utilized to enhance agricultural productivity worldwide. Nevertheless, the unregulated and extreme utilization of pesticides has contaminated food sources and led to pollution in the environment, agriculture, and aquatic systems. However, developing highly efficient in-situ detection and determination of agricultural pesticides and their derivatives is a need of the hours to control pesticide pollution across the globe. Electrochemical sensor performance can be enhanced by immobilizing nanostructures using binder (binder-based) and direct vertically aligned nanostructures (VANs) growth on the functioning electrode surface. Binder-free and binder-based sensors are functionalized by diversely shaped nanostructures for electrochemical sensing of agricultural pesticides using different electrochemical sensing techniques. In binder-based sensors, embedded catalysts are delaminated quickly, which could deter repeatability and reproducibility. Moreover, the binder could potentially interfere, affecting its sensing performance. VANs exhibited high surface area, maximum surface roughness, unimpeded charge transport characteristics, and easy substrate penetration morphologies. VANs could eliminate the problems associated with the quick delamination of catalysts, the need for a binder, and the nanostructure immobilization process. Herein, we have synthesized 1D surface VANs of ZnO on the FTO in a chemical growth method for electrochemical sensing of aniline in tap and river water. The fabricated sensor exhibited a detection limit of 0.193 µM and sensitivity of 0.198 µA. µM-1.cm-2 within the working range of 0-20 µM. However, the synthesis of VANs involves chemical-based methodologies. Therefore, we have developed nature-inspired 2D VANs of ZnO on FTO for electrocatalytic sensing of p-Chloroaniline. The bio-based sensor demonstrates a detection limit of 0.021 µM and sensitivity of 0.194 µA. µM-1.cm-2 within the concentration range of 0-200 µM.
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This study presents a modified polyol synthesis method for producing silver nanorods (AgNRs, length: 861–1345 nm, diameter: 66–107 nm) with preferential growth along the (111) crystal plane. Immobilizing AgNRs on glassy carbon (GC) electrode with Nafion as a binder decreases its charge transfer resistance from 3040 to 129 kΩ and increases its electroactive area from 0.034 to 0.101 cm2. AgNRs/GC electrode exhibited an aniline detection limit of 0.032 μM and sensitivity of 1.48 μA.M−1cm−2 within a linear range of 0–10 μM using square wave voltammetry (SWV). The reaction rate constant of aniline sensing was determined to be 0.08697 s−1. Chlorobenzene, acephate, and chlorpyrifos could not interfere with aniline detection, and a 26 % decrease in peak response was observed after the 10th cycle of aniline sensing. The sensor demonstrated ∼100 % recovery for aniline, comparable to the performance of high-performance liquid chromatography when applied to real-world samples like tap and river water.
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Cr(VI) contamination has become a major threat due to its carcinogenic nature. Therefore, there has been a persistent demand for affordable, sensitive, and quick sensors to monitor the presence of Cr(VI) in aqueous systems. Herein, we have developed blue-fluorescent carbon dots (CDs, 5.2 nm) using green tea leaves, a cost-efficient and eco-friendly approach for fluorescence sensing of Cr(VI). The detection happens due to the construction of a non-luminous complex which led to fluorescence quenching via the inner filter effect (IFE). The limit of detection (LOD) has been as minimal as 0.004 mg/L (s/k = 3). These findings infer CDs as a potential cost-effective nanosensor for Cr(VI) identification in tap water specimens. In another study, bio-based monodispersed AuNPs with an average diameter of 31.2 nm were synthesized using green tea leaves for colorimetric determination of Ni(II) ions through UV-Vis spectroscopy. The colorimetric sensing ability of the AuNPs for Ni(II) ionic identification in aqueous tap water system (0.001 to 1 mg/L) has been quantified in terms of the limit of detection (LOD) and limit of quantification (LOQ) values of 0.001 and 0.005 mg/L respectively.
CO2 Reduction to Value-Added Products
Greenhouse gas emissions are closely linked to the escalating global energy demand. The world seeks sustainable energy technologies to meet this demand and mitigate emissions. Photocatalytic CO2 reduction offers a promising approach by using abundant sunlight and water to convert CO2 into value-added chemicals such as methanol, ethanol formic acid, and methane, mimicking natural photosynthesis in plants. Bio-based methods for synthesizing semiconductor nanoparticles (NPs) offer numerous advantages over traditional chemical-based approaches, including environmental friendliness, cost-effectiveness, one-step synthesis, and the abundant availability of biomaterial sources. Using green pathways for NPs synthesis and incorporating them into CO2 photo-reduction processes could be a promising strategy to curb industrial CO2 emissions. Herein, we have synthesized bio-based CQDs/CdS nanorods composites, In2O3/CdS heterostructures, 0D CDs/CdS QDs composites using Aegle marmelos vegetal extract. Their photocatalytic activities are summarized as:
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The photocatalytic activity of CQDs/CdS(bio) composites for CO2 reduction to methanol with a yield of 1060.52 μmol/g·h (AQE: 7%) under visible light irradiation
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The photocatalytic study of In2O3/CdS(bio) under visible light showed a production rate of 514.44 μmol/g·h (AQY: 4.44%) for HCOOH and 162 μmol/g·h (AQY: 2.54%) for CO, outperforming CdS(bio) and In?O?(bio) by 9 and 6.5 times, respectively
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The photocatalytic activity of CQDs/CdS(bio) composites for CO2 reduction to formic acid achieved a yield of 439.51 μmol/g·h (AQE: 3.81%) under visible light irradiation
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Efficient electrocatalytic reduction of CO2 to value-added chemicals is also a promising and challenging task. The synthesis of low-cost electrocatalysts in an environmentally benign process is the need of the hour. Herein, we have synthesized Cu2O, SnO2 NPs, and template-free 1D Bi2S3 nanorods using S. edule as a reducing and capping agent source. The prepared catalysts were separately decorated on the Toray carbon paper electrode. The electrocatalytic CO2 results are summarized below:
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Cu2O-modified electrodes decrease the charge transfer resistance by 50 folds and catalyze the electrocatalytic CO2 reduction to formate (HCOO‾) with a faradaic efficiency of 65.3–66.6 % within 60 min
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SnO2(bio) NPs modified electrodes converted CO2 to formate (HCOO−) with a faradaic efficiency of 84.0% within 60 min of the chronoamperometric test
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Modified Bi2S3-NRs(bio) electrode exhibited selective HCOO– formation with a faradaic efficiency of 92.3% within 60 min, while the control group showed only 50.9% faradaic efficiency
Membrane Technology for Microbial Wastewater Treatment
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Ceramic membranes are used in many industrial processes due to their excellent physical properties. However, their application in microbial wastewater treatment is limited due to the growth of microbes in the presence of organic pollutants from wastewater in clogged pores. Herein, we have developed a ceramic membrane and modified it with bio-based AgNPs (prepared using S. edule extract) for antimicrobial activity against microbes present in sewage wastewater. AgNPs modification decreased its average pore size and porosity. The pure water flux of bare and AgNPs modified membranes were 8.1±0.09 ×10−4 and 6.33±0.12 ×10−4 m3.m−2.s−1, respectively. The bare membrane showed antimicrobial activity of 37.03±2.73, 52.64±3.49, and 53.03±6.80% against E. coli, S. aureus, and bacterial strains in sewage water, respectively. AgNPs functionalized ceramic membrane completely inhibited the growth of E. coli, S. aureus, and bacterial strains in sewage water during filtration.
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Conventional membrane-based processes are widely used for wastewater treatment, but membrane fouling is a major challenge. Electrically conductive membranes (ECMs) have recently garnered considerable interest due to their potential to mitigate fouling through membrane self-cleaning. Herein, we have synthesized electrically stimulated polyaniline (PANI) and nature-inspired carbon quantum dots-doped PANI (CQDs/PANI) incorporated polysulfone/polyvinylpyrrolidone (PSF/PVP) membranes for wastewater treatment application. Optimized PANI and CQDs/PANI (40% CQDs) based membranes showed highest conductance of 513.4 ± 24.1 and 997.3 ± 29.7 µS and conductivity of 4.23×10-3 and 5.3×10-3 S cm-1, respectively. E. coli-containing wastewater was filtered through the base and modified membranes and exhibited up to 96.5% rejection of E. coli. Further, the used membrane was kept under an electric field (potential) for self-cleaning activity, and ~83.7% flux recovery was observed.
