A facile synthesis of bismuth oxychloride-graphene oxide composite for visible light photocatalysis of aqueous diclofenac sodium

Recent advances in visible light driven inactivation of bloom forming blue-green algae using novel nano-composites: Mechanism, efficiency and fabrication approaches

Over the years, algae have proved to be a water pollutant due to global warming, climate change, and the unregulated addition of organic compounds in water bodies from diffused resources. Harmful algal blooms (HABs) are severely affecting the health of humans and aquatic ecosystems. Among available anti-blooming technologies, semiconductor photocatalysis has come forth as an effective alternative. In the recent past, literature has been modified extensively with a decisive knowledge regarding algal invasion, desired preparation of nanomaterials with enhanced visible light absorption capacity and mechanisms for algal cell denaturation. The motivation behind this review article was to gather algal inactivation data in a systematic way based on various research studies, including the construction of nanoparticles and purposely to test their anti-algal activities under visible irradiation. Additionally, this article mentions variety of starting materials employed for preparation of various nano-powders with focus on their synthesis routes, analytical techniques as well as proposed mechanisms for lost cellular integrity in context of reduced chlorophyll' a' level, cell rapture, cell leakage and damages to other physiological constituents; credited to oxidative damage initiated by reactive oxidation species (ROS). Various floating and recyclable composited catalysts Ag2CO3-N: GO, Ag/AgCl@ZIF-8, Ag2CrO4-g-C3N4-TiO2/mEP proved to be game-changers owing to their enhanced VL absorption, adsorption, stability, separation and reusability. An outlook for the generalized limitations of published reports, cost estimations for practical implementation, issues and challenges faced by nano-photocatalysts and possible opportunities for future studies are also proposed. This review will be able to provide vast insights for coherent fabrication of catalysts, breakthroughs in experimental methodologies and help in elaboration of damage mechanisms.

The mechanism and reaction kinetics of visible light active bismuth oxide deposited on titanium vanadium oxide for aqueous diclofenac photocatalysis

Non-uniform, non-spherical bismuth oxide deposited on titanium vanadium oxide (3%-BVT1) was successfully synthesized via co-precipitation method and assessed for visible light degradation of aqueous diclofenac. The synthesized photocatalysts were characterized using X-ray diffraction, diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, and high-resolution transmission electron microscopy. Up to 80.7% diclofenac degradation was observed with a significant increment in reaction rate compared to commercially available Degussa P25 (kapp = 0.0013 → 0.0083 min-1) achieved within 3 h treatment time under optimized parameters of diclofenac concentration (10 mg L-1), catalyst loading (0.1 g L-1), and pH (5). The enhanced photocatalysis could be due to electron-hole separation and contribution of powerful oxidative species •OH > O2•-  > h+  >  > e-. The recyclability experiments indicate that 3%-BVT1 retained its efficiency up to 74.1% over five reaction cycles. Gas chromatography-mass spectrometry analysis indicated the formation of several transformation products during the degradation pathway. The studies of interfering ions depicted mild interference by sulfates, while interference by phosphates and nitrates was negligible during photocatalytic process, i.e., 70, 78.01, and 78.43% for the selected concentrations of 50, 25, and 40 mg L-1 as per their maximum concentrations detected in the natural wastewaters. Thus, 3%-BVT1 is a potential versatile candidate to treat various organic pollutants including pharmaceuticals.

Graphite/carbon-doped TiO2 nanocomposite synthesized by ultrasound for the degradation of diclofenac

Graphite/C-doped TiO2 nanocomposite was synthesized at room temperature using a simple, impressive, and indirect sonication (20 kHz) by the cup horn system. Tetrabutyltitanate as the precursor of titanium and graphite (G) as the carbon source was used in the preparation of nanocomposite as a photocatalyst. The molar ratio of G/TiO2 as a key parameter was investigated in the synthesis of G/C-doped TiO2. The obtained materials were widely characterized using XRD, SEM, TEM, FTIR, XPS, and UV-Vis diffuse reflectance techniques. The UV-Vis diffuse reflectance spectroscopy results showed that the edge of light absorption of nanocomposite was distinctly red-shifted to the visible area via carbon doping. The XPS outcomes acknowledged the existence of the C, Ti, and O in the photocatalyst. The composite showed an enhancement in the dissociation efficiency of photoinduced charge carriers through the doping process. The photocatalytic activity of the synthesized nanocomposite was checked with diclofenac (DCF) as a pharmaceutical contaminant. The results displayed that G/C-doped TiO2 represented better photocatalytic performance for DCF than TiO2. This was due to the excellent crystallization, intense absorption of visible light, and the impressive separation of photoinduced charge carriers. Various active species such as •OH, •O2¯, h+, and H2O2 play a role in the degradation of DFC. Therefore, different scavengers were used and the role of each one in degradation was investigated. According to the obtained results, •O2¯ radical showed a major role in the photocatalytic process. This work not only proposes a deep insight into the photosensitization-like mechanism by using G-based materials but also develops new photocatalysts for the removal of emerging organic pollutants from waters using sunlight as available cheap energy.

Sb-Doped Cerium Molybdate: An Emerging Material as Dielectric and Photocatalyst for the Removal of Diclofenac Potassium from Aqueous Media

This work reports the influence of antimony substitution in a cerium molybdate lattice for improved dielectric and photocatalytic properties. For this purpose, a series of Ce2-xSbx(MoO4)3 (x = 0.00, 0.01, 0.03, 0.05, 0.07, and 0.09) were synthesized through a co-precipitation route. The as-synthesized materials were characterized for their optical properties, functional groups, chemical oxidation states, structural phases, surface properties, and dielectric characteristics using UV-Vis spectroscopy (UV-Vis), Fourier transform infrared (FTIR) and Raman spectroscopies, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) analysis, and impedance spectroscopy, respectively. UV-Vis study showed a prominent red shift of absorption maxima and a continuous decrease in band gap (3.35 eV to 2.79 eV) by increasing the dopant concentration. The presence of Ce-O and Mo-O-Mo bonds, detected via FTIR and Raman spectroscopies, are confirmed, indicating the successful synthesis of the desired material. The monoclinic phase was dominant in all materials, and the crystallite size was decreased from 40.29 nm to 29.09 nm by increasing the Sb content. A significant increase in the dielectric constant (ε' = 2.856 × 108, 20 Hz) and a decrease in the loss tan (tanδ = 1.647, 20 Hz) were exhibited as functions of the increasing Sb concentration. Furthermore, the photocatalytic efficiency of pristine cerium molybdate was also increased by 1.24 times against diclofenac potassium by incorporating Sb (x = 0.09) in the cerium molybdate. The photocatalytic efficiency of 85.8% was achieved within 180 min of UV light exposure at optimized conditions. The photocatalytic reaction followed pseudo-first-order kinetics with an apparent rate constant of 0.0105 min-1, and the photocatalyst was recyclable with good photocatalytic activity even after five successive runs. Overall, the as-synthesized Sb-doped cerium molybdate material has proven to be a promising candidate for charge storage devices and a sustainable photocatalyst for wastewater treatment.

Impact of graphene oxide on visible light photocatalytic performance of graphene oxide/graphitic carbon nitride three-dimensional structure composites

The non-metallic catalyst graphitic carbon nitride (g-C3N4) has attracted a significant amount of attention due to its excellent photocatalytic performance. The photocatalytic performance of g-C3N4 has been further enhanced by the incorporation of graphene oxide (GO) as a composite catalyst. However, the enrichment and recovery of these two-dimensional composites after photocatalysis is still a difficult challenge. In this work, a visible light responsive graphene oxide/graphitic carbon nitride coated sponge three-dimensional composite (PU-GO/g-C3N4) was prepared by electrostatic self-assembly using polyurethane sponge (PU) as a skeleton and g-C3N4 as a photocatalyst. The degradation rate of rhodamine B (RhB) under visible light was used as an index to evaluate the photocatalytic performance of PU-GO/g-C3N4. The results demonstrate that during the photocatalytic degradation of RhB by PU-GO/g-C3N4, g-C3N4 is the main photocatalyst, while the holes and the superoxide radicals generated by electron excitation are the main agents. As a bridge connecting PU and g-C3N4, GO improves the agglomeration phenomenon of g-C3N4 on PU. Meanwhile, GO has excellent carrier mobility and inhibits the recombination of photogenerated electrons and holes. Moreover, the presence of GO enhances the absorption of light and dyes. Overall, the addition of GO effectively enhances the photocatalytic performance of PU-GO/g-C3N4 due to it enhances dye absorption, improves light energy utilization rate, and expedites transfer of photogenerated electrons. After 5 cycles, PU-GO/g-C3N4 still exhibits an RhB degradation rate of 92.06%, demonstrating good stability and recycling performance. This material shows great promise for practical environmental remediation applications.

Impact of wastewater characteristics on the removal of organic micropollutants by Chlorella sorokiniana

Microalgae-based technologies can be used for the removal of organic micropollutants (OMPs) from different types of wastewater. However, the effect of wastewater characteristics on the removal is still poorly understood. In this study, the removal of sixteen OMPs by Chlorella sorokiniana, cultivated in three types of wastewater (anaerobically digested black water (AnBW), municipal wastewater (MW), and secondary clarified effluent (SCE)), were assessed. During batch operational mode, eleven OMPs were removed from AnBW and MW. When switching from batch to continuous mode (0.8 d HRT), the removal of most OMPs from AnBW and MW decreased, suggesting that a longer retention time enhances the removal of some OMPs. Most OMPs were not removed from SCE since poor nutrient availability limited C. sorokiniana growth. Further correlation analyses between wastewater characteristics, biomass and OMPs removal indicated that the wastewater soluble COD and biomass concentration predominantly affected the removal of OMPs. Lastly, carbon uptake rate had a higher effect on the removal of OMPs than nitrogen and phosphate uptake rate. These data will give an insight on the implementation of microalgae-based technologies for the removal of OMPs in wastewater with varying strengths and nutrient availability.

Investigating the Reduction/Oxidation Reversibility of Graphene Oxide for Photocatalytic Applications

The aim of the study was to analyze the reversibility of the cycle of graphene oxide (GO), reduced GO, and GO obtained by consecutive reoxidation of reduced GO. Accordingly, GO was heated in three different atmospheres (oxidizing, inert, and reducing, i.e., air, nitrogen, and argon/hydrogen mixture, respectively) at 400 °C to obtain reduced GO with varying composition. The bare GO and the RGO samples were oxidized or reoxidized with HNO₃. The thermal properties, composition, bonds, and structure of the samples were investigated with TG/DTA, EDX, Raman spectroscopy, and XRD. Their photocatalytic activity was tested by decomposing methyl orange dye under UV light irradiation.

Fabrication and characterization of pectin-graphene oxide-magnesium ferrite-zinc oxide nanocomposite for photocatalytic degradation of diclofenac in an aqueous solution under visible light irradiation

Wastewater containing pharmaceutical contaminants has become a critical environmental concern due to rising population and drug consumption caused by increased life expectancy. Diclofenac (DCF) is one of the most applicable drugs for veterinary and human health purposes, polluting surface waters in different ways. This work aims to synthesize a novel pectin-graphene oxide (GO)-magnesium ferrite (MgFe₂O₄)-zinc oxide (ZnO) nanocomposite (PGMZ) for photocatalytic degradation of DCF in an aquatic environment under visible light irradiation. The single and synthesized nanocomposites were characterized by several analyses, confirming the successful synthesis of the nanocomposite. Effects of four operation conditions, including nanocomposite dosage (1-1.25 g/L), nanocomposite type, initial contaminant concentration (35-55 mg/L), and solution pH (3-11), were investigated on the degradation performance. From the kinetic study, the effect of mixing two composites, i.e., synergy percentage, was 38.7% when ZnO-MgFe₂O₄ particles were added to the GO-pectin structure. By examining the effect of different free radical enhancers and scavenging compounds on the DCF photodegradation, the most influential scavenging components were in the following order; NaCl > Na₂CO₃ > Na₂SO₄, while K₂S₂O₈ was a better enhancer than H₂O₂ at their optimal concentration. Finally, the PGMZ photocatalyst was reused six times with a reduction of about 20% in its removal efficiency, indicating excellent reusability and stability.

Photocatalytic assessed adsorptive removal of tinidazole from aqueous environment using reduced magnetic graphene oxide-bismuth oxychloride and its silver composite

Antibiotics (tinidazole (TNZ)) in wastewater, exhibit adverse effects on humans and ecosystem. The current study was aimed to synthesize photocatalysts mrGO/BiOCl and mrGO/BiOCl/Ag. mrGO was coupled with BiOCl by hydrothermal method and Ag was deposited over it. The synthesized mrGO/BiOCl and mrGO/BiOCl/Ag were confirmed by Pzc analysis (5.5 and 4.4 for mrGO/BiOCl and mrGO/BiOCl/Ag, respectively), surface area analysis (380 m² g^-1, 227.7 m² g^-1, 220 m² g^-1 for mrGO, mrGO/BiOCl and mrGO/BiOCl/Ag respectively), elemental analysis (Ag, O, Bi, Fe), surface morphology (rough ball like sphere of mrGO/BiOCl and cubic Ag nanoparticles in mrGO/BiOCl/Ag), functional groups and band gap (Eg) determination. The Eg was determined using Kubelka-Munk equation as 3.5 and 2.8 eV for mrGO/BiOCl and mrGO/BiOCl/Ag respectively. During the adsorption study, the best experimental conditions for various operating parameters such as pH (2), contact time (5 min for mrGO/BiOCl and 10 min for mrGO/BiOCl/Ag under UV irradiation), TNZ concentration (18 μgL^-1) and catalyst dosage (0.001 g) were achieved. Kinetic study revealed that both composites followed pseudo second order kinetics (R² = 0.9979 and 0.9986, respectively). Data of rGO/BiOCl was fitted to Freundlich adsorption model (R² = 0.9687) and rGO/BiOCl/Ag fitted to Langmuir adsorption model (R² = 0.9994). Moreover, thermodynamic parameters confirmed that a photodegradation phenomenon was spontaneous and exothermic. The results confirmed that rGO/BiOCl and rGO/BiOCl/Ag are appropriate composites for TNZ removal from the aqueous environment with removal efficiency of 97 and 24%, respectively.

Visible Light-Driven Advanced Oxidation Processes to Remove Emerging Contaminants from Water and Wastewater: a Review

The scientific data review shows that advanced oxidation processes based on the hydroxyl or sulfate radicals are of great interest among the currently conventional water and wastewater treatment methods. Different advanced treatment processes such as photocatalysis, Fenton's reagent, ozonation, and persulfate-based processes were investigated to degrade contaminants of emerging concern (CECs) such as pesticides, personal care products, pharmaceuticals, disinfectants, dyes, and estrogenic substances. This article presents a general overview of visible light-driven advanced oxidation processes for the removal of chlorfenvinphos (organophosphorus insecticide), methylene blue (azo dye), and diclofenac (non-steroidal anti-inflammatory drug). The following visible light-driven treatment methods were reviewed: photocatalysis, sulfate radical oxidation, and photoelectrocatalysis. Visible light, among other sources of energy, is a renewable energy source and an excellent substitute for ultraviolet radiation used in advanced oxidation processes. It creates a high application potential for solar-assisted advanced oxidation processes in water and wastewater technology. Despite numerous publications of advanced oxidation processes (AOPs), more extensive research is needed to investigate the mechanisms of contaminant degradation in the presence of visible light. Therefore, this paper provides an important source of information on the degradation mechanism of emerging contaminants. An important aspect in the work is the analysis of process parameters affecting the degradation process. The initial concentration of CECs, pH, reaction time, and catalyst dosage are discussed and analyzed. Based on a comprehensive survey of previous studies, opportunities for applications of AOPs are presented, highlighting the need for further efforts to address dominant barriers to knowledge acquisition.

Fabricating BiOCl/BiVO4 nanosheets wrapped in a graphene oxide heterojunction composite for detection of an antihistamine in biological samples

Antibiotics are essential medications for human and animal health, as they are used to battle urinary infections and bacterial diseases. Therefore, the rapid determination of antibiotic drugs in biological samples is necessary to address the current clinical challenge. Here, we developed a heterojunction ternary composite of BiOCl/BiVO₄ nanosheets enriched with graphene oxide (BiOCl/BiVO₄@GO) for accurate and minimal-level detection of an antihistamine (promethazine hydrochloride, PMZ) in urine samples. The BiOCl/BiVO₄ nanosheets were prepared by a wet chemical approach using a deep eutectic green solvent. The spectroscopic and analytical methods verified the formation and interaction of the BiOCl/BiVO₄@GO composite. Our results showed that the thoroughly exfoliated BiOCl/BiVO₄@GO composite retained good electrical conductivity and fast charge transfer toward the electrode-electrolyte interface in neutral aqueous media. In addition, the experimental conditions were accurately optimized, and the BiOCl/BiVO₄@GO composite showed excellent electrocatalytic activity toward the oxidation of PMZ. Indeed, the BiOCl/BiVO₄@GO composite demonstrated a good linear response range (0.01-124.7 μM) and a detection level of 3.3 nM with a sensitivity of 1.586 μA μM^-1 cm^-2. In addition, the BiOCl/BiVO₄@GO composite had excellent storage stability, good reproducibility, and reliable selectivity. Finally, the BiOCl/BiVO₄@GO displayed a desirable recovery level of PMZ in urine samples for real-time monitoring.

Facile synthesis of electrocatalytically active bismuth oxide nanosheets for detection of palladium traces in pharmaceutical wastewater

Current synthesis routes of bismuth oxide nanosheets (BiONS) are relatively complicated, requiring the use of halogens or metalloids. Herein, a facile method to synthesize BiONS without the addition of halogens or other metalloids was developed. The synthesized BiONS were identified to have flake-shaped structures (300-1000 nm in width) with the thickness of 6-10 nm, which were predominantly made of β-Bi₂O₃. Such BiONS were applied to modify the surface of screen-printed carbon electrodes (BiONS-SPCEs) for the development of a robust palladium (Pd²⁺) sensor. After optimizing the electrochemical parameters of the sensor, it was found that the linear sensor response range and limit of detection for Pd²⁺ were 40-400 and 1.4 ppb, respectively. The electrocatalytic activity of the Pd²⁺-sensor was validated in the competing environment of other metal and metalloid ions. Real samples collected during a Pd recovery process from pharmaceutical wastewater were used to verify the application of BiONS-SPCEs in control of palladium recovery process. The quantitative results of post recovery palladium concentrations obtained using BiONS-SPCEs in treated pharmaceutical wastewater samples were in good agreement with those obtained by inductively coupled plasma-optical emission spectrometry (ICP-OES). Thus, such Pd²⁺-sensor provided the possibility of on-site process control of complex industrial samples for obtaining near-instant information that would lead to better management of resources used in the process, and same time assure environmental standards for both recovered products and processed discharge.

Bismuth Oxyhalide-Based Materials (BiOX: X = Cl, Br, I) and Their Application in Photoelectrocatalytic Degradation of Organic Pollutants in Water: A Review

An important target of photoelectrocatalysis (PEC) technology is the development of semiconductor-based photoelectrodes capable of absorbing solar energy (visible light) and promoting oxidation and reduction reactions. Bismuth oxyhalide-based materials BiOX (X = Cl, Br, and I) meet these requirements. Their crystalline structure, optical and electronic properties, and photocatalytic activity under visible light mean that these materials can be coupled to other semiconductors to develop novel heterostructures for photoelectrochemical degradation systems. This review provides a general overview of controlled BiOX powder synthesis methods, and discusses the optical and structural features of BiOX-based materials, focusing on heterojunction photoanodes. In addition, it summarizes the most recent applications in this field, particularly photoelectrochemical performance, experimental conditions and degradation efficiencies reported for some organic pollutants (e.g., pharmaceuticals, organic dyes, phenolic derivatives, etc.). Finally, as this review seeks to serve as a guide for the characteristics and various properties of these interesting semiconductors, it discusses future PEC-related challenges to explore.

Diclofenac degradation by activating peroxydisulfate via well-dispersed GO/Cu2O nano-composite

Owing to high treatment efficiency under neutral condition and no extra energy required, copper-mediated activation of persulfate (PS) has been widely used for the degradation of refractory organic pollutants in water. The dispersion stability of copper nanoparticle in water, however, remains a great challenge. Meanwhile, chemical oxidative modification of graphene oxide (GO) can improve the dispersion stability of GO in water. In this paper, cuprous oxide (Cu₂O) was deposited on the surface of GO. GO/Cu₂O nano-composites with different mass ratios, i.e., m(GO):m(Cu₂O) of 1:2, 1:5, 1:10, and 1:25, were prepared. When m(GO):m(Cu₂O) was 1:2, the amount of GO/Cu₂O nano-composite was 1.00 g/L and C_PDS:C_DCF was 15:1, and the catalytic degradation rate of diclofenac (DCF) was up to 90%. Corresponding physicochemical properties of the resulting samples were comprehensively characterized by using SEM, TEM, XRD, Raman, FT-IR, and XPS. DCF degradation by activating peroxydisulfate (PDS) via GO/Cu₂O nano-composite was also investigated in detail. It is found that the synergistic effect, namely GO adsorption and multivalent copper ion electron transfer, makes GO/Cu₂O nano-composite reveal higher reactivity. Moreover, GO/Cu₂O nano-composite possesses good stability in consecutive cycling test. EPR analyses shows that ·OH and SO₄^·- radicals are involved in DCF degradation. It is indicated that the DCF degradation process contain hydroxylation and the cleavage of C-N bond, which is explored by GC-MS. In our research, well-dispersed GO/Cu₂O nano-composite with high capacity and good cycling stability was fabricated successfully. Compared with pure Cu₂O nanoparticle, GO/Cu₂O nano-composite exhibits the better performance for DCF removal. A novel well-dispersed cuprous oxide (Cu₂O) deposited on surface of GO was fabricated with high catalytic performance. Its heterogeneous activation of peroxydisulfate (PDS) for diclofenac (DCF) degradation was investigated. GO/Cu₂O nano-composite was proved high capacity and good cycling stability. Meanwhile, the possible DCF degradation pathway was explored. Compared with pure Cu₂O nanoparticle, GO/Cu₂O nano-composite exhibits better performance for DCF removal.

Predicting the trend and utility of different photocatalysts for degradation of pharmaceutically active compounds: A special emphasis on photocatalytic materials, modifications, and performance comparison

The rapid rise in the healthcare sector has led to an increase in pharmaceutically active compounds (PhACs) in different aqueous bodies. The toxicity of the PhACs and their ability to persist after conventional treatment processes have escalated research in the field of photocatalytic treatment. Although different photocatalysts have been successful in degrading PhACs, their inherent drawbacks have severely limited their application on a large scale. A substantial amount of research has been aimed at overcoming the high cost of the photocatalytic material, low quantum yield, the formation of toxic end products, etc. Hence, to further research in this field, researchers must have a fair idea of the current trends in the application of different photocatalysts. In this article, the trends in the use of various photocatalysts for the removal of different PhACs have been circumscribed. The performance of different groups of photocatalysts to degrade PhACs from synthetic and real wastewater has been addressed. The drawbacks and advantages of these materials have been compared, and their future in the field of PhACs removal has been predicted using S-curve analysis. Zinc and titanium-based photocatalysts were efficient under UV irradiation, while bismuth and graphene-based materials exhibited exemplary performance in visible light. However, iron-based compounds were found to have the most promising future, which may be because of their magnetic properties, easy availability, low bandgap, etc. Different modification techniques, such as morphology modification, doping, heterojunction formation, etc., have also been discussed. This study may help researchers to clarify the current research status in the field of photocatalytic treatment of PhACs and provide valuable information for future research.

Bismuth-Graphene Nanohybrids: Synthesis, Reaction Mechanisms, and Photocatalytic Applications—A Review

Photocatalysis is a classical solution to energy conversion and environmental pollution control problems. In photocatalysis, the development and exploration of new visible light catalysts and their synthesis and modification strategies are crucial. It is also essential to understand the mechanism of these reactions in the various reaction media. Recently, bismuth and graphene’s unique geometrical and electronic properties have attracted considerable attention in photocatalysis. This review summarizes bismuth-graphene nanohybrids’ synthetic processes with various design considerations, fundamental mechanisms of action, heterogeneous photocatalysis, benefits, and challenges. Some key applications in energy conversion and environmental pollution control are discussed, such as CO2 reduction, water splitting, pollutant degradation, disinfection, and organic transformations. The detailed perspective of bismuth-graphene nanohybrids’ applications in various research fields presented herein should be of equal interest to academic and industrial scientists.