Enhanced detoxification of p-bromophenol by novel Zr/Ag-TiO2@rGO ternary composite: Degradation kinetics and phytotoxicity evolution studies

Evaluating efficacy of Pseudomonas sp. EN-4 to lower the toxic potential of 4-bromophenol and assessing its competency in simulated microcosm

An indigenous bacterium Pseudomonas sp. EN-4 had been reported earlier for its ability to co-metabolise 4-bromophenol (4-BP), in presence of phenol (100 mg/L) as co-substrate. The present study was undertaken to validate the efficacy of biotransformation by comparing the toxicity profiles of untreated and EN-4 transformed samples of 4-BP, using both plant and animal model. The toxicity studies in Allium cepa (A. cepa) indicated to lowering of mitotic index (MI) from 12.77% (water) to 3.33% in A. cepa bulbs exposed to 4-BP + phenol, which reflects the cytotoxic nature of these compounds. However, the MI value significantly improves to 11.36% in its biologically treated counterpart, indicating normal cell growth. This was further supported by significant reduction in chromosomal aberrations in A. cepa root cells exposed to biologically treated samples of 4-BP as compared to untreated controls. The oxidative stress assessed by comparing the activity profiles of different marker enzymes showed that the activities of superoxide dismutase (SOD), ascorbate peroxidase (APX) and guaiacol peroxidase (GPX) were reduced by 56%, 72%, and 37% respectively, in EN-4 transformed samples of 4-BP + phenol compared to its untreated counterpart. Similar trends were evident in the comet assay of fish (Channa punctatus) blood cells exposed to untreated and biologically treated samples of 4-BP. The comparative studies showed significant reduction in tail length (72.70%) and % tail intensity (56.15%) in fish blood cells exposed to EN-4 treated 4-BP + phenol, compared to its untreated counterpart. The soil microcosm studies validated the competency of the EN-4 cells to establish and transform 4-BP in soil polluted with 4-BP (20 mg/kg) and 4-BP + phenol (20 + 100 mg/kg). The isolate EN-4 achieved 98.08% transformation of 4-BP in non-sterile microcosm supplemented with phenol, indicating to potential of EN-4 cells to establish along with indigenous microflora.

A novel BiOCl (110)/rGO/Ag3PO4 (111) heterostructure for efficient detoxification of 2,4-dichlorophenol

An effective method using nontoxic and efficient photocatalysts are crucial for wastewater treatment. Bismuth oxychloride (BiOCl) is considered as one of the valuable photocatalysts due to its unique layered plate like structure, however higher recombination and unsatisfied visible light absorption efficiency seriously affecting its applications. Addition of tetrahedral silver phosphate (Ag₃PO₄) which is known for its superior photocatalytic efficiency under visible light is believed to be the solution for the issue. Upon further adding of reduced graphene oxide (rGO) could form a bridging structure and enhance the activity. Considering the merits of these materials the BiOCl (110)/rGO/Ag₃PO₄ (111) heterojunction has been successfully constructed for 2,4-dichlorophenol (DCP) enhanced detoxification. The efficiency in degradation was found to be 94.8% by BiOCl/rGO/Ag₃PO₄ (k = 0.01879 min^-1) that was greater to that of pure Ag₃PO₄ (∼1.9 times; k = 0.00818 min^-1) and pure BiOCl (∼2.8 times; k = 0.00642 min^-1) after 60 min of visible light irradiation. The mechanism of degradation was explained through the principle of heterojunction energy-band theory. Furthermore, 2,4-dichlorophenol (2,4-DCP) degradation products identification was carried out by ESI/LC-MS to propose the degradation pathway. Furthermore, the phytotoxicity of the intermediate products was investigated by estimating the germination index (GI) values on Phaseolus vulgaris (P. vulgaris) at different time intervals and the GI values were found to be 10.79% and 80.17% before and after degradation respectively. Thus, our results revealed that efficient and significant toxicity reduction was observed in this photodegradation.

Valorization of phenol contaminated wastewater for lipid production by Rhodosporidium toruloides 9564T

Phenol is one of the most common hazardous organic compound presents in several industrial effluents which directly affects the aquatic environment. The present study envisaged the phenol biodegradation and simultaneous lipid production along with its underlying mechanism by oleaginous yeast Rhodosporidium toruloides 9564^T. Experiments were designed using simulated wastewater by varying phenol concentration in the range of 0.25-1.5 g/L and inoculum size of 1, 5, and 10% with and without glucose. The oleaginous yeast was found to completely degrade up to 0.75 g/L phenol with lipid accumulation of 26.3%. Phenol at > 0.5 g/L severely inhibited the growth of R. toruloides 9564^T at 1% and 5% inoculum size. Phenol toxicity up to 0.75 g/L can be overcome by increasing inoculum size to 10%. The maximum specific growth rate (μ_max) and phenol degradation rate (q_max) were found to be 0.0717 h^-1 and 0.01523 h^-1, respectively. The enzymatic pathway study suggested that R. toruloides 9564^T follows an ortho cleavage pathway for phenol degradation and lipid accumulation. Phytotoxicty and cytotoxicity tests for treated and untreated samples clearly demonstrated a decline in toxicity of the treated wastewater. R. toruloides brought about an important paradigm shift toward a circular economy in which industrial wastewater is considered a valuable resource for bioenergy production.

Remediation of pesticides using TiO2 based photocatalytic strategies: A review

Nowadays, pesticides are regarded as the most dangerous of the various organic pollutants, posing substantial environmental and human threats worldwide. Pesticide contamination has become one of the most crucial environmental issues due to its bio-persistence and bioaccumulation. Different conventional methods are being utilized for pesticide removal, yet pesticides are thought to be significantly present in the environment. The development and application of sophisticated wastewater treatment methods are being pursued to remove contaminants effectively, particularly pesticides. In the past several decades, nanoscience and nanotechnology have emerged as essential tools for the identification, removal, and mineralization of persistent pesticides by employing advanced nanomaterials such as pristine titanium dioxide (TiO₂), doped TiO₂, nanocomposites (NCs) TiO₂, and ternary nanocomposites (TNCs) TiO₂ by advanced oxidation processes (AOPs). Advancement in the characteristics of TiO₂ by doping, co-doping, construction of NCs and TNCs has contributed to the dramatic efficiency up-gradation by reducing band gap, solar active photocatalyst, enhancing PCA, high photostability, chemically inertness and multiple time reusability. Based on previous literature, utilizing La-TiO₂ NCs photocatalyst, the mineralization of pesticide (imidacloprid) attained up to 98.17% that is almost 40-53% greater than pristine TiO₂. The present review attempt to discuss the recent research performed on TiO₂ based nanoparticles (NPs) and NCs for photocatalytic mineralization of various pesticides. The basic mechanism of TiO₂ photocatalysis, types of reactors used for photocatalysis, and optimized experimental conditions of TiO₂ for pesticides mineralization are discussed.

Effect of magnetization on the adsorptive removal of an emerging contaminant ciprofloxacin by magnetic acid activated carbon

Magnetic acid activated carbons (MAAC) were prepared from the shells of Sterculia villosa Roxb by activating the biomass and magnetizing it using the co-precipitation technique. Characterization of MAAC prior and post adsorption was performed using various microscopic and spectroscopic analytical techniques, and they verified the formation of magnetic aggregates over porous activated carbon surface. Vibrating Sample Magnetometer (VSM) analysis confirmed the superparamagnetic behaviour of the adsorbent with saturation magnetization (Ms) value of 18.2 emu/g, causing an easy and rapid recovery from the adsorption setup in the presence of an external magnetic field. Langmuir isotherm and pseudo-second-order kinetic model best fit the experimental data with theoretical Langmuir maximum adsorption capacity as 81.97 mg/g and verifying chemisorption type of adsorption process, respectively. Thermodynamic analysis verified the interaction among adsorbate and adsorbent as endothermic, spontaneous, and thermodynamically favourable. Co-existing metal cations showed a significant reduction in ciprofloxacin removal efficiency; co-existing anions, though, showed a negligible influence on the adsorption efficiency of MAAC. Recyclability studies verified that the adsorption efficiency fell from 98% in the first cycle to 43% in the fifth cycle. The Ms value fell to 7.6 emu/g (after five adsorption cycles), affecting the adsorbent's recovery. The Phyto-toxicological assessment was performed to evaluate the environmental risk to human and aquatic life using Vigna mungo seeds. MAAC proved to be an effective and magnetically separable adsorbent for removing antibiotics.

NO3- photolysis-induced advanced reduction process removes NO3- and 2, 4, 6-tribromophenol

Reductive processes are an important type of pollutant removal technology, particularly for organic halogens. NO₃^- is an anion and pollutant that is commonly present in wastewater. In this study, a novel advanced reduction process (ARP) induced by NO₃^- photolysis was developed to remove 2,4,6-tribromophenol (TBP) and NO₃^-. The UV/NO₃^-/formate acid (FA) process achieved NO₃^- removal and improved the debromination of TBP (initial TBP concentration = 0.1 mM) (up to 97.8%), however, their coexistence adversely affected the reductive removal of each component. Acidic conditions (pH 3 in this study) benefited the removal of NO₃^- and the debromination of TBP. Cl^- promoted NO₃^- removal in UV/NO₃^-/FA, however, it decreased the debromination effect of TBP by 27.8%. Humic acid, a typical dissolved organic matter, suppressed NO₃^- removal, TBP degradation and debromination under all experimental conditions. Methyl viologen significantly inhibited the performance of ARP, and this verified the role of CO₂^•- in this ARP. Insufficient reduction and over-reduction of NO₃^- were observed under different conditions and a greater amount of NH₄⁺ was formed under the influence of TBP. The data also indicated that as much as 80% of the removed NO₃^- was converted to NO₂^-, and this is noteworthy. Due to the reductive radicals generated from the oxidation of FA, both oxidative and reductive products of TBP were detected in the effluent. The results of this study provide a potential technology for the reductive removal of organic halogens from NO₃^--rich wastewater.

Novel magnetically separable tetrahedral Ag3PO4/NrGO/CuFe2O4 photocatalyst for efficient detoxification of 2,4-dichlorophenol

An effective as well as eco-friendly photodegradation methods by atoxic and easily reusable photocatalysts are essential for wastewater treatment. Silver phosphate (Ag₃PO₄) specifically in tetrahedral shape is one of the superior catalysts under visible light but its photocorrosion, poor electron transfer ability and low surface adsorption properties limits its applications. Combination of Ag₃PO₄ and nitrogen doped reduced graphene oxide (NrGO) having higher in surface area, ample functional groups and hetero atom doping is expected to get over the problem. Further addition of a spinel ferrite (CuFe₂O₄) could enhance the visible light response activity and helps in easy separation of catalyst for reuse. Given the merits of Ag₃PO₄, NrGO and CuFe₂O₄ we rationally integrated a novel magnetically separable stable Ag₃PO₄/NrGO/CuFe₂O₄ photocatalyst for efficient detoxification of 2,4-dichlorophenol (2,4-DCP). About 95.3% degradation efficiency was achieved by Ag₃PO₄/NrGO/CuFe₂O₄ (k = 0.01978 min^-1) which was ~2.6 times higher than pure Ag₃PO₄ (k = 0.00747 min^-1) in 60 min of visible light irradiation. The Ag₃PO₄/NrGO/CuFe₂O₄ heterojunction was able to separate and recycle easily using an external magnetic field due to its strong magnetism, and after 5 recycles it showed 88.6% of degradation efficiency revealed its higher stability and recyclability. The photocatalytic mechanism of Ag₃PO₄/NrGO/CuFe₂O₄ was explained by heterojunction energy-band theory. In addition, the plausible intermediate products of 2,4-dichlorophenol were analyzed by ESI/LC-MS and proposed the pathway. Moreover, the phytotoxicity was also studied on V. radiata in which GI (germination index) was found to be 11.97% before degradation, while 80.31% of GI was observed in 60 min of degradation which revealed that more significant reduction in toxicity was attained on this photodegradation.

A detailed insight on fabricated porous chitosan in eliminating synthetic anionic dyes from single and multi-adsorptive systems with related studies

Chitosan was fabricated via gelation method using CaBr₂.xH₂O/methanol solution and was studied as a potential adsorbent (MCh) in adsorbing anionic synthetic dyes like Bromophenol blue (BB), Direct blue 6 (DB) and Congo red (CR) from single (one dye species at a time) and multi (having two dyes; binary and all three dyes; tertiary) adsorptive systems. Physico-chemical modifications of MCh surface prior and post modification and dye adsorption were evaluated using scanning electron microscopy, Energy-dispersive X-ray spectroscopy, powder X-ray diffraction analysis, surface area analysis and Fourier-transformed infrared spectroscopy. Influential parameters influencing the adsorption process viz. initial pH of dye solution, MCh dosage, adsorption temperature and initial concentration of dye species were optimised. Adsorptive studies involving single adsorptive setups verified formation of sorbate's (dye species) monolayer over the sorbent's (MCh) surface via chemisorption; as established by Langmuir isotherm and pseudo-second order kinetics model analysis. Theoretical maximum adsorption capacities of MCh for BB, DB and CR was found to be 81.301 mg/g, 163.934 mg/g and 75.758 mg/g, respectively. Meanwhile, for all multi-adsorptive systems, competitive Langmuir isotherm model verified antagonistic behaviour of an individual dye over other dye adsorption over MCh surface in their respective adsorptive systems. Thermodynamics of the sorbate-sorbent interaction was exothermic, spontaneous, with elevated degree of disorderedness; concluding the interaction as thermodynamically favourable. Co-existing metal cations and anionic salts had minimal effect on MCh's adsorption efficiency. Phytotoxicity assay via germination of Vigna mungo seeds verified the efficacy of the adsorbent in eliminating the dye species from single and multi-adsorptive systems.

Facile synthesis of ZnO nanoparticles by Actinidia deliciosa fruit peel extract: Bactericidal, anticancer and detoxification properties

Synthesis of nanoparticles by eco-friendly method pulled an extensive concern worldwide due its biocompatibility and wide range of applications as catalysts, microbicidal agents, cancer treatment, sensors etc. Though different chemical methods available for preparation of ZnO nanoparticles, synthesis by utilizing plant material is an excellent substitute and green method as well. The present study describes preparation of ZnO nanoparticles by low-cost green synthetic way using Actinidia deliciosa (kiwi) fruit peel extract and its excellent biological and catalytic properties. The synthesized nanoparticles were well characterized by UV visible spectroscopy, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM) and Energy-dispersive X-ray spectroscopy (EDAX). The bactericidal activity of the ZnO nanoparticles was determined by using Staphylococcus aureus (S. aureus), while mechanism of cell death was studied by SEM images. Superior anticancer activity was also observed in inhibiting the colon cancer cells (HCT116) by the ZnO nanoparticles. In addition, ZnO nanoparticles showed efficient photocatalytic activity towards degradation of p-bromophenol, about 96.3% within 120 min. Furthermore, phytotoxicity of the intermediate products was analyzed using Vigna radiata (V. radiata) as a model plant. About 8.0% of germination index (GI) was observed in pure p-BP while it increased to 82.3%, and exhibited that the detoxification of p-BP was attained after 120 min of degradation. Thus, the present study demonstrates ZnO nanoparticles prepared from simple, rapid, inexpensive, eco-friendly and efficient green method gives alternative root for biomedicine and wastewater treatment technologies.

The CO2 photoconversion over reduced graphene oxide based on Ag/TiO2 photocatalyst in an advanced meso-scale continuous-flow photochemical reactor

This study aims at examining the use of an advanced meso-scale continuous-flow photochemical reactor for the photocatalytic conversion of CO₂ with water into fuel over TiO₂ (P25), Ag/TiO₂, and Ag/TiO₂/RGO catalysts. The silver loaded photocatalysts were prepared by one-step process via hydrothermal method. The prepared photocatalysts were characterized by various characterization techniques in order to identify the morphological, chemical, physical, and optical properties. The photocatalytic activity of the as-prepared catalysts was firstly examined by the photoelectrochemical (PEC) measurements and secondly by the photocatalytic reduction of CO₂ in the proposed setup. Liquid products were analyzed using gas chromatography-mass spectrometry (GC-MS) and total organic carbon (TOC) techniques. It was found that the ternary composite revealed an outstanding performance towards CO₂ photocatalytic reduction, where its selectivity was directed towards methanol production. The incorporation of graphene nanosheets enhanced the photocatalytic reduction of CO₂ by 3.3 and 9.4 times compared with Ag/TiO₂ and bare TiO₂, respectively, using the proposed photochemical reactor in a continuous mode. This study sheds the light on a novel type of a photocatalytic reactor where CO₂ conversion over Ag/TiO₂/RGO ternary composite was evaluated. A meso-scale continuous-flow photochemical reactor.

rGO-ZnO nanocomposites as efficient photocatalyst for degradation of 4-BP and DEP using high temperature refluxing method in in-situ condition

Persistent organic pollutants (mainly aromatic compounds) such as bromophenol and diethyl phthalate are dangerous and act as primary contaminants in aqueous system. In this study, efficient reduced graphene oxide zinc oxide (rGO-ZnO) nanocomposites were synthesized by using a simple and facile method for photocatalytic degradation of 4-Bromophenol (4-BP) and diethyl phthalate (DEP). The rGO-ZnO (rGZ) nanocomposites (NCs) with different weight ratio of rGO and ZnO (coded as rGZ-1, rGZ-2, rGZ-5 and rGZ-10) were synthesized via high temperature refluxing method. The crystalline structure and phase, surface morphological study, optical properties, crystal defects and existence of functional groups in rGZ NCs were studied by X-ray diffraction (XRD), field-emission-scanning electron microscope (FE-SEM), UV-Visible diffuse reflectance spectroscopy (DRS), Raman spectroscopy and FT-IR analysis, respectively. The elimination of 4-BP and DEP from water by UV-light exposure was considered to estimate the photocatalytic efficiency of prepared rGZ NCs. The maximum elimination of 4-BP and DEP via photodegradation (advanced oxidation process) was found about 99.04% and 98.63% over rGZ NCs after 180 min UV irradiation, respectively. The photodegradation study was examined by using high performance liquid chromatography (HPLC) technique. This study confirms the efficient photocatalytic activity of rGZ-5 towards degradation of 4-BP and DEP. Finally, degradation mechanism has been proposed for the degradation of 4-BP and DEP.

Surface treated acid-activated carbon for adsorption of anionic azo dyes from single and binary adsorptive systems: A detail insight

Current study deals with the surface modification of acid activated carbon (prepared from Pongamia pinnata shells) with Cetyltrimethylammonium bromide (CTAB) and its role as an adsorbent in eliminating anionic azo dyes viz. Congo red (CR) and Direct blue 6 (DB) from single and binary adsorptive systems. Binary adsorptive system involved the synergistic and antagonistic influence of one dye over the adsorption of other dye. Physico-chemical alterations due to surfactant modification and post adsorption were studied using atomic force microscopy (AFM), Zeta Potential, scanning electron microscopy (SEM), Energy-dispersive X-ray spectroscopy (EDS), surface area analysis and Fourier-transformed infrared spectroscopy (FTIR). Process parameters influencing efficient adsorption of CR and DB species viz. initial pH of dye solution, adsorbent dosage, incubation temperature and initial concentration of dye species were optimised. Sorbate-sorbent interaction studies for single adsorptive system revealed sorbate's monolayer formation over adsorbent's surface and the involvement of chemisorption, as verified by Langmuir isotherm model and pseudo-second order model, respectively. Langmuir maximum adsorption capacity of the adsorbent was 555.56 mg/g for CR and 625.00 mg/g for DB. Meanwhile, for binary adsorptive system, competitive Langmuir model verified both CR and DB had antagonistic/competitive effect over each other's adsorption. Thermodynamic analysis revealed the adsorptive process as exothermic, spontaneous and thermodynamically favourable with an elevated degree of dis-orderedness. Co-existing cations and anions has nominal effect on the adsorption capacity of dyes. Recyclability studies verified a modest efficiency of 62.52% for CR and 50.47% for DB species after the end of 4th adsorption-desorption cycle; thus affirming its recyclability potential. Phytotoxic assay affirmed the effectivity of the adsorbent in adsorbing dye species from aqueous solutions using Vigna mungo seeds as the model.

Shuttle-like CeO2/g-C3N4 composite combined with persulfate for the enhanced photocatalytic degradation of norfloxacin under visible light

In this work, the shuttle-like CeO₂ modified g-C₃N₄ composite was synthesized and was combined with persulfate (PS) for the efficient photocatalytic degradation of norfloxacin (NOR) under visible light. Scanning and transmission electron microscopy (SEM and TEM), X-ray diffraction (XRD), UV-vis diffuse reflectance spectroscopy (DRS) and photoluminescence (PL) emission spectra were used to characterize the structural and optical properties of the as-prepared catalysts. Active species trapping experiments demonstrated that additional sulfate radicals (·SO₄^-) formed upon the addition of PS which could cooperate with superoxide radicals (O₂^-), holes (h⁺) and hydroxyl radicals (OH) to decompose NOR. Singlet oxygen (¹O₂) was also formed during the reaction and acted as an important active species. The degradation products of NOR were also identified and analyzed by using LC-MS technology, and the possible degradation mechanism and pathways were proposed and discussed. This work indicated that the shuttle-like CeO₂ modified g-C₃N₄ coupled with PS displayed promising applications in the field of pharmaceutical wastewater purification.