Polyaniline-Coated TiO2 Nanorods for Photocatalytic Degradation of Bisphenol A in Water

Nanocomposite from tannery sludge-derived biochar and Zinc oxide nanoparticles for photocatalytic degradation of Bisphenol A toward dual environmental benefits

The growing concern over the presence of pollutants like Bisphenol A (BPA) in water sources has led to the growth of novel treatment technologies for its removal. This research work investigates the development of a novel biochar-metal oxide nanocomposite derived from tannery sludge and Zinc oxide (ZnO) nanoparticles for the photodegradation of BPA. The biochar was obtained by pyrolysis process, followed by impregnation of ZnO nanoparticles using a hydrothermal technique. The critical properties of as-prepared nanocomposite were evaluated by FT-IR, BET surface area, XRD, FE-SEM, HR-TEM, XPS, PL, EPR, and Raman Spectroscopy. In addition, the photocatalytic activity of nanocomposites was evaluated by measuring the degradation of BPA in visible light irradiation. The outcomes revealed that ZnO-loaded chemically activated biochar exhibited higher photocatalytic activity for the degradation of BPA than the pristine and non-chemically activated biochar. At pH 5, 0.2 g/L of photocatalyst dosage, 20 ppm of initial pollutant concentration, and 150 min of contact time, the maximum degradation efficiency of BPA was observed as 94.50 %. Also, nanocomposites showed good stability and reusability, with only a slight decrease in photocatalytic activity after multiple cycles of use. More importantly, the degradation mechanisms of BPA using as-prepared nanocomposites were analyzed in detail, indicating that the observed photocatalytic activity could be attributed to the synergistic effect between the biochar and ZnO, which provided a large surface area for the adsorption of BPA and promoted the generation of reactive oxygen species for its degradation. Overall, this study highlighted the potential of using nanocomposites from tannery sludge-derived biochar and ZnO nanoparticles for the degradation of BPA from polluted water sources using a photocatalytic process toward the dual environmental benefits.

Preparation of PANI modified TiO2 and characterization under pre- and post- photocatalytic conditions

Polyaniline (PANI) is a promising conducting polymer for surface modification of TiO2 to overcome limitations of the use of visible light and attain increased photocatalytic efficiency for the removal of organic contaminants. In this study, a series of polyaniline modified TiO2 (PANI-TiO2) composites were prepared by using "in-situ" chemical oxidation polymerization method. The composites were systematically characterized by Fourier transform infrared spectroscopy (equipped with an attenuated total reflection accessory, FTIR-ATR), Raman spectroscopy, X-ray diffractometry (XRD), scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM-EDAX), X-ray photoelectron spectroscopy (XPS), ultraviolet-visible diffuse reflectance spectroscopy (UV-DRS), photoluminescence spectroscopy (PL), nitrogen (N2) physisorption (Brunauer - Emmett - Teller surface area (SBET) and Barrett-Joyner-Halenda (BJH) pore size analysis), thermogravimetry-derivative thermogravimetry (TG-DTG) techniques. XRD patterns of PANI-TiO2 composites confirmed both the amorphous phase of PANI and the crystalline character of TiO2. TG/DTG analysis complemented the XRD profiles that the interactions between PANI and TiO2 resulted in a more stable PANI-TiO2 matrix. SEM images displayed the dominant morphology as dandelion-like shapes of PANI being more pronounced with increasing PANI ratios in PANI-TiO2 composites. UV-DRS profiles revealed that the band gap energies of the composites were lower than bare TiO2 expressing a shift to the visible light region. Both PL and UV-DRS analyses confirmed the band-gap reduction phenomenon of PANI modification of TiO2. The incorporation of PANI into TiO2 resulted in a reduction of the surface area of TiO2. The composites were subsequently subjected to photocatalytic activity assessment tests using humic acid (HA) as a model of refractory organic matter (RfOM) under simulated solar irradiation (Uyguner-Demirel et al. Environ Sci Pollut Res 30 85626-85638, 2023). The morphological and structural changes attained upon application of photocatalysis were also evaluated by FTIR-ATR, Raman spectroscopy, XRD, and SEM-EDAX methods in a comparable manner. The FTIR-ATR spectral features of PANI, RfOM and all composites displayed peaks with slight shifts under pre- and post- photocatalytic conditions as well as following dark surface interactions. Besides exhibiting noticeable photocatalytic performance, PANI-TiO2 composites were also proven to maintain stability under non-selective oxidation conditions in the presence of a complex organic matrix. The prepared PANI-TiO2 composites overcoming the limitations of UVA light active bare TiO2 photocatalysis could possibly find a beneficial use as potential catalysts in solar photocatalytic applications.

Enhanced and Proficient Soft Template Array of Polyaniline-TiO2 Nanocomposites Fibers Prepared Using Anionic Surfactant for Fuel Cell Hydrogen Storage

Porous TiO2-doped polyaniline and polyaniline nanocomposite fibers prepared by the in situ polymerization technique using anionic surfactant in an ice bath were studied. The prepared nanocomposites were characterized by FTIR spectroscopy and XRD patterns for structural analysis. The surface morphology of the polyaniline and its nanocomposites was examined using SEM images. DC conductivity shows the three levels of conductivity inherent in a semiconductor. Among the nanocomposites, the maximum DC conductivity is 5.6 S/cm for 3 wt.% polyaniline-TiO2 nanocomposite. Cyclic voltammetry shows the properties of PANI due to the redox peaks of 0.93 V and 0.24 V. Both peaks are due to the redox transition of PANI from the semiconductor to the conductive state. The hydrogen absorption capacity is approximately 4.5 wt.%, but at 60 °C the capacity doubles to approximately 7.3 wt.%. Conversely, 3 wt.% PANI-TiO2 nanocomposites have a high absorption capacity of 10.4 wt.% compared to other nanocomposites. An overall desorption capacity of 10.4 wt.% reduced to 96% was found for 3 wt.% TiO2-doped PANI nanocomposites.

A systematic review of photocatalytic degradation of humic acid in aqueous solution using nanoparticles

OBJECTIVES

Humic acid (HA) compounds in the disinfection processes of drinking water and wastewater are considered as precursors of highly toxic, carcinogenic and mutagenic disinfectant by-products. The aim of this study was to systematically review all research studies on the photocatalytic degradation of humic acid and to evaluate the laboratory conditions and results of these studies.

CONTENT

The present systematic review was performed by searching the Scopus, PubMed, and web of science databases until December 2021. The parameters of type of catalyst, catalyst size, optimum pH, optimum initial concentration of humic Acid, optimum catalyst concentration, optimum time, light used and removal efficiency were investigated.

SUMMARY

395 studies were screened and using the inclusion and exclusion criteria, in total, 20 studies met our inclusion criteria and provided the information necessary to Photocatalytic degradation of humic acid by nanoparticles. In the investigated studies, the percentage of photocatalytic degradation of humic acid by nanoparticles was reported to be above 70%, and in some studies, the removal efficiency had reached 100%.

OUTLOOK

From the results of this systematic review, it was concluded that the photocatalytic process using nanoparticles has a high effect on the degradation of humic acid.

Easy synthesis of PPy/TiO2/ZnO composites with superior photocatalytic performance, efficient supercapacitors and nitrite sensor

The synthesis of Polypyrrole (PPy)/TiO2/ZnO composites involved a chemical oxidative polymerization process, wherein the addition of TiO2/ZnO was varied from 1 to 10 wt%. The composites' photocatalytic capabilities, supercapacitor performance, and potential use as a nitrite sensor were thoroughly assessed, alongside investigations into their photoluminescence (PL) and morphological characteristics. The strong interaction between TiO2/ZnO and PPy was confirmed using FTIR, UV-Vis, and PL spectroscopy techniques. The composites demonstrated aggregated and spherical-shaped morphological features investigated by FESEM. Such morphological structures of the composites were distinct from the TiO2/ZnO (rod-like) and similar to PPy structure (spherical). However, such composites showed dominating spherical-shaped morphology ensuring a diameter in the range of 50-200 nm. The PPy/TiO2/ZnO composites exhibited significantly enhanced photocatalytic efficiency in methylene blue (MB) removal, achieving a range of 88-93% compared to PPy alone, which only achieved 77.2% MB removal. The Cyclic Voltammetry (CV) data exhibited a promising hybrid supercapacitor performance of the composites with a high capacitance value, good energy density, as well as an excellent power density. The fabricated supercapacitor was capable of lightened up a single red 5 mm LED for a few minutes, indicating the commendable energy storage capacity. A newly developed PPy/TiO2/ZnO composite is potentially used to develop as a sensor probe for the detection of nitrite chemicals using the linear sweep voltammetry (LSV) technique in three electrodes system in room conditions. It is found an excellent sensor results in terms of sensitivity as well as detection limit and satisfactory results when validated with the real samples. These results offer novel insights into the fabrication of PPy/TiO2/ZnO photocatalysts for addressing organic waste treatment, while also presenting promising prospects for potential applications in supercapacitors and sensors.

Photocatalytic performance of PANI modified TiO2: Degradation of refractory organic matter

Surface modification of TiO2 with polyaniline (PANI) conducting polymer has been used to achieve visible light photoresponse, thereby increasing solar photocatalytic activity. In this study, photocatalytic performances of PANI-TiO2 composites with different mole ratios were synthesized by the in situ chemical oxidation polymerization method and tested for the degradation of a model refractory organic matter (RfOM), namely humic acid in an aqueous medium under simulated solar irradiation in a comparative manner. Adsorptive interactions under dark conditions and interactions under irradiation were investigated as contributing factors to photocatalysis. Degradation of RfOM was monitored in terms of UV-vis parameters (Color436, UV365, UV280, and UV254) and fluorescence spectroscopic parameters as well as the mineralization extent by dissolved organic carbon contents. The presence of PANI exerted an enhancement in photocatalytic degradation efficiency compared to pristine TiO2. The synergistic effect was more pronounced in lower PANI ratios whereas higher PANI ratios reflected a retardation effect. Degradation kinetics were assessed by pseudo-first-order kinetic model. For all UV-vis parameters analyzed, highest and lowest rate constants (k) were attained in the presence of PT-14 (2.093 × 10-2 to 2.750 × 10-2 min-1) and PT-81 (5.47 × 10-3 to 8.52 × 10-3 min-1), respectively. Variations in selected absorbance quotients, i.e., A254/A436, A280/A436, and A253/A203, were distinctive and compared with respect to irradiation time and photocatalyst type. Upon use of PT-14, a steady decreasing profile with respect to irradiation time was attained for A253/A203 quotient as 0.76-0.61, followed by a rapid decrease to 0.19 in 120 min. The incorporation effect of PANI into TiO2 composite could be visualized in A280/A365 and A254/A365 quotients exhibiting an almost constant and parallel trend. As a general trend, decrease in the major fluorophoric intensity FIsyn,470 with photocatalysis was observed under extended irradiation conditions; however, an abrupt decline was remarkable in the presence of PT-14 and PT-18. Fluorescence intensity decrease correlated well with spectroscopic evaluation of rate constants. A thorough evaluation of spectroscopic parameters of UV-vis and fluorescence can provide significant information for practical applications in control of RfOM in water treatment.

Highly customized porous TiO2-PANI nanoparticles with excellent photocatalytic efficiency for dye degradation

The present work encompasses a simple strategy to synthesize highly porous TiO₂ by incorporating PANI polymer into the sol-gel chemistry of Titanium dioxide/Titanium (IV)-iso-propoxide (TiO₂/TTIP). A series of TiO₂ samples by varying wt.% of PANI, have been synthesized. A probable growth mechanism has been presented for the formation of a porous ginger-like nanostructure of TiO₂-PANI (TP). HRTEM images reveal that the particle size range is 6-16 nm for pristine TiO₂ and 5-13 nm for TP samples. XPS analysis confirms the presence of the hydrogen bonds in-between surface hydroxyl groups (Ti-OH) of TiO₂ and the protonated nitrogen of PANI. UV-visible absorption study reveals a small shift towards longer wavelength for TP8 sample than that of pristine TiO₂ (λ_max = 314 nm) as well as reduction in E_g value from 3.02 eV to 2.89 eV. FTIR results confirm the successful interaction of PANI and TiO₂. BJH and BET analysis confirms an increase of porosity in TP8 sample with an average pore volume of 0.36 cm³ g^-1. High photocatalytic activity (98.77%) towards Methylene blue dye degradation is observed for TP8 sample having 8 wt% of PANI and it is explained through the combined effect of structural porosity of TiO₂ and synergic effect of PANI. The K_appa value at pH 11 (0.01372 min^-1) is found to be 7.84-folds higher than that of the photocatalytic reaction at pH 3 (K_appa = 0.00175 min^-1). While pristine TiO₂ exhibits the minimum removal efficiency (89.57%) with K_appa of 0.00756 min^-1. K_appa value of catalysis reaction for TP8 is found to be almost 2-fold higher than pristine TiO₂. Quantum Yield value for TP8 is found to be 3.59 × 10^-4 molecules photon^-1. This high Quantum Yield value of present photocatalytic system explicates the low energy consumption for the treatment of textile dye pollutant. Additionally, STY value (1.79 × 10^-5 molecules photon^-1 mg^-1) confirms the outstanding mineralization strength of TP8 by a unit mass for high amounts of MB dye per unit time. Thus, the present study offers an excellent photocatalyst i.e., TP8 having 8 wt% of PANI for the degradation of MB dye.

Current progress in treatment technologies for plastic waste (bisphenol A) in aquatic environment: Occurrence, toxicity and remediation mechanisms

Bisphenol-A (BPA) is a type of endocrine disrupting compound (EDC) that is being widely used in the production of polycarbonate and epoxy resins. In the last few years, human exposure to BPA has been extensively high due to the continuous increment in the Annual Growth Rate (AGR) of the BPA global market. The presence and transportation of BPA in the environment could cause serious damage to aquatic life and human health. This paper reviewed the literature on the exposure and toxicity mechanisms of BPA and advanced analytical techniques for the detection of BPA in the environment and human beings. The study indicated that BPA can cause damaging effects on numerous tissues and organs, including the reproductive system, metabolic dysfunction, respiratory system, immune system and central nervous system. On the basis of reported studies on animals, it appears that the exposure of BPA can be carcinogenic and responsible for causing a variety of cancers like ovarian cancer, uterine cancer, prostate cancer, testicular cancer, and liver cancer. This review paper focused mainly on the current progress in BPA removal technologies within last ten years (2012-2022). This paper presents a comprehensive overview of individual removal technologies, including adsorption, photocatalysis/photodegradation, ozonation/advance oxidation, photo-fenton, membranes/nanofilters, and biodegradation, along with removal mechanisms. The extensive literature study shows that each technology has its own removal mechanism and their respective limitations in BPA treatment. In adsorption and membrane separation process, most of BPA has been treated by electrostatic interaction, hydrogen boning and π-π interations mechanism. Whereas in the degradation mechanism, O* and OH* species have played a major role in BPA removal. Some factors could alter the removal potential and efficiency of BPA removal. This review paper will provide a useful guide in providing directions for future investigation to address the problem of BPA-containing wastewater treatment.

Plasmonic enhanced photocatalytic activity of Ag/TiO2 tube-in-tube fibers

Ag nanoparticle was found to significantly enhance the photocatalytic activity of self-organized TiO₂ nanotube structures. Herein, novel Ag/TiO₂ tube-in-tube fibers have been prepared by a facile electrospinning technology and calcination process. Employed as the photocatalyst, the composite could efficiently catalyze the photodegradation of the model organic pollutant, rhodamine B under visible light irradiation, exhibiting a superior photocatalytic activity than the undoped TiO₂ tube-in-tube fibers. This enhanced activity has been ascribed to plasmonic characteristics of Ag nanoparticles, which promote the light absorption and charge transfer feasibility. The simple, low-cost and green fabrication route of the composite provides a novel means for preparing similar materials, holding great promise for wider application in the future.

Role of polyaniline in accomplishing a sustainable environment: recent trends in polyaniline for eradicating hazardous pollutants

Attaining a sustainable environment has become a prime area of research interest, as it is an utmost necessity for a healthy life. Hence, ample studies have been carried out in adopting different processes and utilizing various materials to attain the goal. Herein, we present an exclusive discussion on one such material, i.e., polyaniline (PANI) and its derivatives. Being an intrinsic conducting type, it has grabbed more attention due to its durability in different doped/un-doped states, promptness in structural alteration, and solution processability. This review presents an exhaustive discussion on published reports showing utilization of PANI and its derivative in various forms like pure and composites, for cleaning the environment through adsorption, photodegradation, etc., and the various methods adopted in order to achieve an optimum operating condition to obtain the maximum outcome. In addition to these merits and demerits, various technical challenges faced with materials have been also presented. Therefore, it is expected that this piece of work, presenting the exhaustive discussion on PANI and; its derivatives would help to develop a better understanding of this excellent conducting polymer PANI and provide a state of art on the role of this material for attaining sustainable surroundings for the living beings.

Conductive polymer layered semiconductor for degradation of triclopyr acid and 2,4-dichlorophenoxyacetic acid from aqueous stream using coalesce adsorption-photocatalysis technique

Polyaniline supported titanium dioxide nanoparticles (PTs) were fabricated using chemical oxidative aniline polymerization in the presence of titanium dioxide with ammonium peroxydisulfate as an oxidant. The synthesized PTs were thoroughly characterized for their morphological and functional features. PTs were employed for the photodegradation of acidic herbicides; 2,4-dichlorophenoxyacetic acid (2,4-D) and triclopyr acid (TCP). PT's surface modifications were imparted and their herbicide removal efficiencies were compared. The best operating conditions for adsorption/photocatalysis were 0.5 g/L photocatalyst, 10 mg/L concentration of individual herbicides resulted in 90.72% removal of TCP at pH 4 and 99.91% removal of 2,4-D at pH 5. Adsorption kinetics of herbicides, onto PT-1 showed the equilibrium attainment within 30 min and experimental data obeyed pseudo-second order model for TCP and 2,4-D removal which was governed by chemisorption. Analysis of TCP and 2,4-D adsorption indicated that the removal followed Sips model for TCP removal while Redlich-Peterson model explained the removal of 2,4-D by PT-1. Rate constants indicated that the amount of TiO₂ in the PTs played an important role in removing the herbicides and PT-1 material excellent remarkable activity for three cycles of photodegradation. Thus, this work reports the polymerization of aniline onto TiO₂ and their utility as photocatalyst for the expulsion of 2,4-D and TCP from water.

Recent developments in photocatalysis of industrial effluents ։ A review and example of phenolic compounds degradation

Industrial expansion and increased water consumption have created water scarcity concerns. Meanwhile, conventional wastewater purification methods have failed to degrade recalcitrant pollutants efficiently. The present review paper discusses the recent advances and challenges in photocatalytic processes applied for industrial effluents treatment, with respect to phenolic compounds degradation. Key operational parameters including the catalyst loading, light intensity, initial pollutants concentration, pH, and type and concentrations of oxidants are evaluated and discussed. Compared to the other examined controlling parameters, pH has the highest effect on the photo-oxidation of contaminants by means of the photocatalyst ionization degree and surface charge. Furthermore, major phenolic compounds derived from industrial sources are comprehensively presented and the applicability of photocatalytic processes and the barriers in practical applications, including high energy demand, technical challenges, photocatalyst stability, and recyclability have been explored. The importance of energy consumption and operational costs for realistic large-scale processes are also discussed. Finally, research gaps in this area and the suggested direction for improving degradation efficiencies in industrial applications are presented. In the light of these premises, selective degradation processes in real water matrices such as untreated sewage are proposed.

Highly efficient, bioactive, and bifunctional sorbent p-n-p visible light heterogeneous photocatalyst utilizing ultra-fine ZnS nanoparticles embedded in a polymeric nanocomposite

This study reports the successful synthesis of a ZnS@GO@Pani polymeric nanocomposite (NC) via chemical polymerization. The product was used for simultaneous photocatalytic degradation-adsorption of malachite green (MG), a carcinogenic and widely used dye. The physicochemical properties of the prepared NC were characterized by various techniques. Morphological and XRD results confirmed the fine size of ZnS nanoparticles (NPs) with an approximate mean size of 5 nm, uniformly distributed within the polymeric matrix. For comparative purposes, photocatalytic dye degradation-adsorption of this nanohybrid was explored both in the dark and under natural light. It was observed that 0.1 g of the ternary NC in MG aqueous solution (20 ppm) leads to dye adsorption within 15 minutes with an efficiency of 70% under dark conditions. Also, MG removal efficiency of up to 90% was achieved in 15 minutes under natural light owing to integrated photocatalytic degradation-adsorption mechanisms. Adsorption isotherm studies were performed considering Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich (D-R) models. The results showed that the Freundlich isotherm with R 2 = 0.988 is well consistent with the experimental data. Integrated photocatalytic degradation-adsorption kinetics were modeled with pseudo-first-order (PFO) and pseudo-second-order (PSO) models where PSO with R 2 = 0.999 best fitted the data, implying the predominant role of chemical adsorption in the dye removal process. Antibacterial tests revealed superior antibacterial activity of the prepared ZnS@GO@Pani NC against both Gram-negative and Gram-positive bacteria, demonstrating the remarkable synergistic effect of ZnS NPs embedded in the GO@Pani matrix. Accordingly, the prepared NC could be regarded as a promising candidate for wastewater treatment applications. The leaching and regeneration studies also confirmed that the prepared NC is a non-toxic dye removal agent with good reusability.

Characterization of South African Brewery Wastewater: Oxidation-Reduction Potential Variation

Conventional wastewater treatment processes are challenged by the need to effectively reduce pollutant loads before disposal or reuse, as the composition and concentration of contaminants in brewery wastewater change with time. This results in the variation of the oxidation-reduction potential (ORP) of the affluent. Hence, the current study is aimed at the application of ORP as a real-time tool to monitor brewery wastewater quality. Other physicochemical parameters of the local brewery in South Africa investigated included temperature (T), pH, conductivity, turbidity, total chemical oxygen demand (TCOD), soluble chemical oxygen demand (SCOD), particulate chemical oxygen demand (PCOD), total solids, orthophosphate, ammoniacal nitrogen, total Kjeldahl nitrogen (TKN), total nitrogen (TN), nitrate, and nitrite nitrogen. It was found that the ORP decreased (135 to −305 mV) with an increase in alkalinity (pH 4.4 to 12.2) with linear regression coefficient fit (R2 = 0.9994). The ORP facilitated the wastewater nutrient constituent degradability which improved the water quality. Furthermore, the high organic content of the brewery wastewater was found as measured by total COD (3447–11,813 mg/L). This suggests remediation before reuse of the brewery wastewater will require a robust integrated wastewater treatment process.

Kaolin-graphene carboxyl incorporated TiO2 as efficient visible light active photocatalyst for the degradation of cefuroxime sodium

A novel solar light active photocatalyst, TiO₂/kaolin-graphene carboxyl nanocomposite was synthesized by hydrothermal method for the degradation of cephalosporin antibiotic, cefuroxime sodium. The synthesized photocatalyst was characterized by various analytical and spectroscopic techniques, including Fourier transform infrared spectroscopy (FT-IR), powder X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX) thermogravimetry (TG), UV-Vis diffuse reflectance spectroscopy (DRS) and photoluminescence (PL). The prepared TiO₂/kaolin-graphene carboxyl nanocomposite exhibited efficient photocatalytic degradation of methylene blue (MB) upon illumination with the solar simulator as compared to unmodified TiO₂. The incorporation of both kaolin and graphene carboxyl was found to immobilize TiO₂, enhancing the visible light absorption range of TiO₂. Scavenger study revealed that hydroxyl radicals act as the main active species in the photocatalytic degradation process. The hydroxyl group present on kaolin surface reacts with photo-generated holes to increase the amount of hydroxyl radical, and further the graphene carboxyl plays a role to impede the recombination of photo-generated electron-hole pairs. Furthermore, the synthesized photocatalyst was found to degrade cefuroxime sodium within 90 min of sunlight illumination, indicating that TiO₂/kaolin-graphene carboxyl nanocomposites would be very beneficial for pharmaceutical waste management through the advanced oxidation process. Mass spectral analysis was also carried out for elucidating the photocatalytic degradation pathway of cefuroxime sodium.

An Overview of Polymer-Supported Catalysts for Wastewater Treatment through Light-Driven Processes

In recent years, alarm has been raised due to the presence of chemical contaminants of emerging concern (CECs) in water. This concern is due to the risks associated with their exposure, even in small amounts. These complex compounds cannot be removed or degraded by existing technologies in wastewater treatment plants. Therefore, advanced oxidation processes have been studied, with the objective of developing a technology capable of complementing the conventional water treatment plants. Heterogenous photocatalysis stands out for being a cost-effective and environmentally friendly process. However, its most common form (with suspended catalytic particles) requires time-consuming and costly downstream processes. Therefore, the heterogeneous photocatalysis process with a supported catalyst is preferable. Among the available supports, polymeric ones stand out due to their favorable characteristics, such as their transparency, flexibility and stability. This is a relatively novel process; therefore, there are still some gaps in the scientific knowledge. Thus, this review article aims to gather the existing information about this process and verify which questions are still to be answered.

Nitrogen doped carbon spheres from Tamarindus indica shell decorated with vanadium pentoxide; photoelectrochemical water splitting, photochemical hydrogen evolution & degradation of Bisphenol A

At present energy and environmental remediation are of highest priority for the well defined sustainability. Multifunctional materials that solve both the issues are on high demand. In the present work, a simple method has been followed to extract carbon spheres fromTamarindus indica(commonly known astamarind fruit) shelland doped with nitrogen (N-CS). Vanadium pentoxide nanoflakes were decorated aroundN-CS and the resultant is labeled as V₂O₅/N-CS nanocomposite. The spectroscopic, microscopic, elemental mapping and x-ray photoelectron spectroscopic characterization confirm the nitrogen doping and formation of hybrid material. N-CS, V₂O₅, and V₂O₅/N-CS nanocompositehave been evaluated for their efficiency to evolve hydrogen and for degradation of Bisphenol A (BPA) under visible light. In addition, electrocatalytic hydrogen evolution in presence of light has also been evaluated. The DRS spectrum proves the decrease in the bandgap of V₂O₅ upon its decoration around N-CS material. In a photochemical experiment, the V₂O₅/N-CS nanocomposite evolved 18,600 μmolg^-1 of H_2.Electrochemical hydrogen evolution has also been evaluated in presence of light and obtained the onset potential of -60mV with 52 mV dec^-1 Tafel slope value. Scavenger studies indicate superoxide radicals and hydroxyl radicals are the active species responsible for the degradation of BPA. BPA degradation pathway has been predicted with the support of LC-MS results of the intermediates. All these results indicate the synthesized nanocomposite could be an efficient, stable multifunctional material for photocatalytic applications.

One-Pot Synthesis of Long Rutile TiO2 Nanorods and Their Photocatalytic Activity for O2 Evolution: Comparison with Near-Spherical Nanoparticles

Rutile TiO₂ nanorods with lengths greater than 600 nm and aspect ratios greater than ca. 16 were synthesized through a one-pot hydrothermal method using lactic acid (LA) as a structure-directing agent. Under the hydrothermal treatment at 200 °C, the LA concentration higher than 1.6 mol dm^-3 and the hydrothermal time of 72 h were needed to obtain 100% rutile nanorods. The length and the width of the nanorods increased with the increasing LA concentration. The photocatalytic activity of the synthesized nanorods was evaluated for the oxygen evolution in aqueous AgNO₃ solutions under ultraviolet irradiation. Calcination of the synthesized nanorods at 400 °C was required to decompose residual organic compounds on the surface and improve the oxygen evolution. The highest oxygen evolution rate was obtained with the nanorods after being calcined at 800 °C. It is worth noting that the nanorods retained their shape (aspect ratio of 8.8) at 800 °C. Selected area electron diffraction patterns indicated that the side or the end surface of the nanorods was attributable to the {110} or {111} facet, respectively. Deposition of Pt or PbO₂ on the nanorods revealed that the {110} or {111} facet acted as reductive or oxidative sites. For comparison, near-spherical TiO₂ nanoparticles were synthesized by a sol-gel method. Furthermore, using glycolic acid as the structure-directing agent, we synthesized small rutile TiO₂ nanorods (aspect ratio of 9) and changed the shape to near-spherical (aspect ratio of 1.3) by calcining at 800 °C. Time-resolved diffuse reflectance spectra were measured to determine the lifetime of the photogenerated electrons. The photocatalytic activity of the nanorods was much lower than that of the near-spherical TiO₂ nanoparticles. However, the nanorods synthesized with LA are useful as catalyst support or platforms for various applications because of their unique morphology and high heat resistance.

Advanced Photocatalysts Based on Conducting Polymer/Metal Oxide Composites for Environmental Applications

Photocatalysts provide a sustainable method of treating organic pollutants in wastewater and converting greenhouse gases. Many studies have been published on this topic in recent years, which signifies the great interest and attention that this topic inspires in the community, as well as in scientists. Composite photocatalysts based on conducting polymers and metal oxides have emerged as novel and promising photoactive materials. It has been demonstrated that conducting polymers can substantially improve the photocatalytic efficiency of metal oxides owing to their superior photocatalytic activities, high conductivities, and unique electrochemical and optical properties. Consequently, conducting polymer/metal oxide composites exhibit a high photoresponse and possess a higher surface area allowing for visible light absorption, low recombination of charge carriers, and high photocatalytic performance. Herein, we provide an overview of recent advances in the development of conducting polymer/metal oxide composite photocatalysts for organic pollutant degradation and CO2 conversion through photocatalytic processes.