Synthesis of WO3 nanofibers decorated with BiOCl nanosheets for photocatalytic degradation of organic pollutants under visible light

Photocatalytic boron nitride-based nanomaterials for the removal of selected organic and inorganic contaminants in aqueous solution: A review

Boron nitride (BN) coupled with various conventional and advanced photocatalysts has been demonstrated to exhibit extraordinary activity for photocatalytic degradation because of its unique properties, including a high surface area, constant wide-bandgap semiconducting property, high thermal-oxidation resistance, good hydrogen-adsorption performance, and high chemical/mechanical stability. However, only limited reviews have discussed the application of BN or BN-based nanomaterials as innovative photocatalysts, and it does not cover the recent results and the developments on the application of BN-based nanomaterials for water purification. Herein, we present a complete review of the present findings on the photocatalytic degradation of different contaminants by various BN-based nanomaterials. This review includes the following: (i) the degradation behavior of different BN-based photocatalysts for various contaminants, such as selected dye compounds, pharmaceuticals, personal care products, pesticides, and inorganics; (ii) the stability/reusability of BN-based photocatalysts; and (iii) brief discussion for research areas/future studies on BN-based photocatalysts.

Plasmonic-driven charge separation through combining Ag nanoparticles (Ag NPs) to form a double Z-scheme heterostructure in WO3/BiOCl/g-C3N4 for the photocatalytic degradation of antibiotics

Integrating a heterojunction system with the impact of surface plasmon resonance (SPR) is an executable and innovative tactic for photocatalyst amelioration. Ag nanoparticle (Ag NP)-modified WO3/BiOCl/g-C3N4 (WB-CN) was favorably fabricated through in situ photo deposition assembly to form double heterojunctions (A-WBCN). The degradation performance of A-WBCN is better than that of pure g-C3N4 (CN) and WO3/BiOCl (WB), it can degrade more than 90% of OFLX within 20 minutes, due to Ag NPs performing as a bridge for electron mediators, apart from the implications of SPR in A-WBCN. The results of UV diffuse reflectance spectroscopy indicate that loading with Ag NPs can expand the light absorption range of WB-CN to near-infrared. The photoluminescence spectra and transient photocurrent spectra indicate that Ag NP loading significantly improves the separation efficiency of photogenerated carriers. Density functional theory (DFT) simulation results show that the introduction of Ag NPs can change the direction of carrier movement, resulting in bending of the energy bands of WB and CN, improving the redox ability of A-WBCN, and improving its photocatalytic efficiency. In addition, the intermediate products of OFLX was determined by HPLC-MS analysis. The spin electron resonance (ESR) results indicate that ˙O2- and ˙OH are the main active species in photocatalytic degradation. This work furnishes a fresh idea for upgrading photocatalytic performance and advancing electron transfer.

Construction of a Z-scheme Ag2MoO4/BiOBr heterojunction for photocatalytically removing organic pollutants

How to facilitate photogenerated-carrier separation is an important step in developing excellent semiconductor photocatalysts for environmental pollutant removal. Herein, Ag₂MoO₄ (AMO) nanoparticles were assembled onto the surface of BiOBr (BOB) nanosheets to construct a highly efficient Z-scheme AMO/BOB heterojunction photocatalyst. Several analytical techniques were used to elucidate the characteristics and photocatalytic mechanism of the AMO/BOB heterojunction. Photodegradation experiments for removing methylene blue under simulated-sunlight irradiation reveal that a 20%AMO/BOB heterojunction exhibits excellent photodegradation activity with η(30 min) = 93.8% and k_app = 0.08638 min^-1, which were greater by 4.5 and 5.6 times in comparison with that of pure BOB and AMO, respectively. Based on the experimental and density functional theory (DFT) calculation results, it is proposed that the Z-scheme carrier transfer/separation mechanism dominates the enhanced photodegradation performance of the composite photocatalysts. Additionally, the potential application of AMO/BOB photocatalysts in degrading various organic pollutants (including organic dyes, antibiotics and other serious organic pollutants) was also investigated.

Panax notoginseng powder -assisted preparation of carbon-quantum-dots/BiOCl with enriched oxygen vacancies and boosted photocatalytic performance

Low activity of photocatalysts is a serious bottleneck to the practical application of photocatalytic technology. In this paper, a series of BiOCl composite photocatalysts containing carbon quantum dots (CQDs) were successfully prepared by adding Panax notoginseng powder (PNP) to the solvothermal synthesis system of BiOCl as a template agent and a raw material for 0D CQDs. CQDs/BiOCl exhibit 2D flake structures and 3D flower-like microspheres self-assembled from thin flakes, holding rich oxygen vacancies (OVs). After detailed characterization, it was found that the amount of OVs on BiOCl could be regulated according to the amount of PNP added. The CQDs/OVs-BiOCl photocatalysts exhibit higher photogenerated charge separation efficiency and photocatalytic activity than the bare BiOCl. When the mass ratio of PNP/BiOCl is 1.0%, the photocatalyst demonstrates the maximum degradation activity for rhodamine B (RhB) and perfluorooctanoic acid (PFOA). In view of the solid observations, a photocatalytic enhancement mechanism of CQDs/BiOCl was elucidated.

Electrospun composite nanofibers as novel high-performance and visible-light photocatalysts for removal of environmental pollutants: A review

Environmental pollution caused by industries and human manipulations is coming a serious global challenge. On the other hand, the world is facing an energy crisis caused by population growth. Designing solar-driven photocatalysts which are inspired by the photosynthesis of plant leaves is a fantastic solution to use solar energy as green, available, and unlimited energy containing ∼50% visible light for the removal of environmental pollutants. The polymeric and non-polymeric-based electrospun composite nanofibers (NFs) are as innovative photocatalytic candidates which increase photocatalytic activity and transition from UV light to visible light and overcome the aggregation, photocorrosion, toxicity, and hard recycling and separation of the nanosized powder form of photocatalysts. The composite NFs are fabricated easily by either embedding the photocatalytic agents into the NFs during electrospinning or via their decorating on the surface of NFs post-electrospinning. Polyacrylonitrile-based, tungsten trioxide-based, zinc oxide-based, and titanium dioxide-based composite NFs were revealed as the most reported composite NFs. All the lately investigated electrospun composite NFs indicated long-term stability, high photocatalytic efficiency (∼> 80%) within a short time of light radiation (10-430 min), and high stability after several cycles of use. They were applied in various applications including degradation of dyes/antibiotics, water splitting, wastewater treatment, antibacterial usage, etc. The photogenerated species especially holes, O₂^∙-, and ^.OH were mostly responsible for the photocatalytic mechanism and pathway. The electrospun composite NFs have the potential to use in large-scale productions in condition that their thickness and recycling conditions are optimized, and their toxicity and detaching are resolved.

Preparation, Characterization and Application of Epitaxial Grown BiOBr (110) Film on ZnFe2O4 Surface with Enhanced Photocatalytic Fenton Oxidation Properties

A novel BiOBr photocatalyst was epitaxially grown in situ onto the surface of ZnFe₂O₄, a ferroelectric material with a strong polarization effect. The formatted BiOBr/ZnFe₂O₄ composite (BOB/ZFO) showed excellent photocatalytic degradation performance of tetracycline antibiotics (TCs). One of the composites with ZnFe₂O₄ content of 10% (BOB/ZFO-10) showed the best properties; the degradation efficiency of TCs upon visible light irradiation for 180 min was 99.2%, which was 3.58 times higher than that of pure phase BiOBr. The functions of ZnFe₂O₄ are assumed to be such that the addition of this ferroeletric material not only regulated the spontaneous polarization of BiOBr in the process of synthesis, but also resulted in the construction of Z-scheme heterostructures due to the appropriate staggered band structure of BiOBr and ZnFe₂O₄. In the presence of ferroelectric material ZnFe₂O₄, the local structure of BiOBr may be distorted accordingly, resulting in preferential growth of a (110) crystal facet of BiOBr and enhancement of spontaneous polarization, which promotes the efficient separation of photogenerated electron-hole pairs of ZnFe₂O₄ and BiOBr, and therefore enhances the redox capacity of the photocatalytic degradation of organic pollutants.

Donor–acceptor organic nanostructure based on conjugated polymer for improving visible-light-driven photocatalytic activity towards degradation of dye in aqueous medium

Hybrid donor–acceptor nanostructures based on P3HT with improved light harvesting properties were employed for organic dye degradation.

Ag-SPR and semiconductor interface effect on a ternary CuO@Ag@Bi2S3 Z-scheme catalyst for enhanced removal of HIV drugs and (photo)catalytic activity

The development of ternary composites has gained great interest as they can be used as a catalyst due to the different semiconductors with the variation in the band edge positions creates a potential gradient at the composite interface.

Size controlled silver nanoparticles on β-cyclodextrin/graphitic carbon nitride: an excellent nanohybrid material for SERS and catalytic applications

A nanohybrid (NH), having high dispersion of silver nanoparticles (AgNPs) on β-cyclodextrin (β-CD)/graphitic carbon nitride (g-CN), designated as AgNPs/β-CD/g-CN-NH, was synthesized and characterized. It was exploited for a couple of environmental remediation applications like SERS sensing and catalytic reduction of specific organic pollutants in water. It showed excellent SERS activity as a Raman probe for the detection of malachite green (MG). Its enhancement factor (EF) and detection limit for MG were equal to 7.26 × 10⁶ and 1 × 10^-9 M, respectively. The relative standard deviation (RSD) was equal to 3.8% which indicates high homogeneity of AgNP dispersion and signal reproducibility of the SERS substrate. The NH displayed high catalytic activity for the reduction of eosin yellow (EY) in the presence of NaBH₄ with the rate constant (k) of 0.1142 min^-1. A comparison of the present NH with other reported materials reveals better SERS and catalytic activities of the former than those of the latter. The SERS activity of the NH was also examined for sensing of other triphenylamine dyes like methyl violet (MV), and it was successful. The same NH also exhibited high catalytic activity towards the reduction of Congo red (CR). The results of both studies clarify that the NH is an excellent SERS substrate and efficient catalyst for the detection of organic environmental pollutants having structures similar to MG and their degradation. This is due to the distribution of the controlled size of AgNPs on g-CN promoted by β-CD. Therefore, we focus our attention on future environmental applications of the nanohybrid as a very cheap SERS substrate and a very active catalyst.

ZnFe2O4@WO3-X /Polypyrrole: An Efficient Ternary Photocatalytic System for Energy and Environmental Application

Environmental protection and the necessity of green energy have become fundamental concerns for humankind. However, rapid recombination of photoexcitons in semiconductors often gets in the path of photocatalytic reactions and annoyingly suppresses the photocatalytic activity. In this study, a polypyrrole (PPY)-supported step-scheme (S-scheme) ZnFe₂O₄@WO_3-X (PZFW15) ternary composite was fabricated by a multistep process: hydrothermal and calcination processes, followed by polymerization. During the formation of the heterojunction, the oxygen vacancy (OV) on WO_3-X promotes effective separation and increases the redox power of the photogenerated excitons via the built-in internal electric field of S-scheme pathways between ZnF and WO_3-X. The successful construction of the S-scheme heterojunction was substantiated through X-ray photoelectron spectroscopy, experimental calculations, radical trapping experiment, and liquid electron spin resonance (ESR) characterization, whereas the existence of OVs was well confirmed by EPR and Raman analyses. Meanwhile, the PPY served as a supporter, and the polaron and bipolaron species of PPY acted as electron and hole acceptors, respectively, which further enhances the charge-carrier transmission and separation in the ternary PZFW15 photocatalyst. The designed ternary nanohybrid (PZFW15) displays outstanding gemifloxacin detoxification (95%, 60 min) and hydrogen generation (657 μmol h^-1), i.e., 1.5 and 2.2 times higher than the normal S-scheme ZFW15 heterostructure and pure ZnFe₂O₄ (ZnF), respectively, with an apparent conversion efficiency of 4.92%. The ESR and trapping experiments indicate that the generated ^•OH and ^•O₂ ^- radicals from the PZFW15 photocatalyst are responsible for gemifloxacin degradation. This unique PPY-supported S-scheme heterojunction is also beneficial for the enhanced electron-transfer rate and provides abundant active sites for photocatalytic reactions.

WO3/Ag2CO3 Mixed Photocatalyst with Enhanced Photocatalytic Activity for Organic Dye Degradation

The development of an efficient photocatalyst with superior activity under visible light has been regarded as a significant strategy for pollutant degradation and environmental remediation. Herein, a series of WO₃/Ag₂CO₃ mixed photocatalysts with different proportions were prepared by a simple mixing method and characterized by XRD, SEM, TEM, XPS, and DRS techniques. The photocatalytic performance of the WO₃/Ag₂CO₃ mixed photocatalyst was investigated by the degradation of rhodamine B (RhB) under visible light irradiation (λ > 400 nm). The photocatalytic efficiency of the mixed WO₃/Ag₂CO₃ photocatalyst was rapidly increased with the proportion of Ag₂CO₃ up to 5%. The degradation percentage of RhB by WO₃/Ag₂CO₃-5% reached 99.7% within 8 min. The pseudo-first-order reaction rate constant of WO₃/Ag₂CO₃-5% (0.9591 min^-1) was 118- and 14-fold higher than those of WO₃ (0.0081 min^-1) and Ag₂CO₃ (0.0663 min^-1). The catalytic activities of the mixed photocatalysts are not only higher than those of the WO₃ and Ag₂CO₃ but also higher than that of the WO₃/Ag₂CO₃ composite prepared by the precipitation method. The activity enhancement may be because of the easier separation of photogenerated electron-hole pairs. The photocatalytic mechanism was investigated by free radical capture performance and fluorescence measurement. It was found that light-induced holes (h⁺) was the major active species and superoxide radicals (·O₂ ^-) also played a certain role in photocatalytic degradation of RhB.

Insight in to sunlight-driven rapid photocatalytic degradation of organic dyes by hexacyanoferrate-based nanoparticles

Release of colouring agents into the environment alarms the need to design a cheap, quick and safe process. Owing to environmental safety concern, synthesis of two metal hexacyanoferrates (MHCFs) based on cadmium (CdHCF) and manganese (MnHCF) was carried out using natural plant extract of Azadirachta indica and water as a solvent. Synthesized MHCFs were utilized for the removal of an acid dye (fuchsin acid, FA) and a xanthenes dye (rhodamine B, RB). The reactions were optimized at various conditions of dye concentration, catalyst dose, reaction pH, time and source of light. The MHCFs showed excellent results with both the dyes within very limited span of time (2 h). Consequently, 98% of FA and 97% of RB were degraded with 10 mg of CdHCF, at neutral pH and under sunlight. The degradation process followed the first-order reaction kinetics having t_1/2 around 0.3 min. The MHCFs exhibited difference of only little percentage in degradation owing to a very slight difference between their surface areas (CdHCF: 54.1 m² g^-1; MnHCF: 49.7 m² g^-1). The synthesised nanocatalysts were stable as indicated by their higher negative zeta potential values. The adsorption of dyes was found to be maximum with CdHCF having X_m value 19.69 mg g^-1 and 18.15 mg g^-1 for FA and RB, respectively. Photocatalytic degradation involved the main role of hydroxyl radical as indicated by decline in activity of nanocatalyst in the presence of scavengers. All in all, this study presents highly active nanomaterials with higher surface area, stability and semiconducting properties under natural conditions.

Facile synthesis of a heterostructured lanthanum-doped SnO2 anchored with rGO for asymmetric supercapacitors and photocatalytic dye degradation

Owing to its good redox properties, excellent electron–hole pair generation, wide band gap and outstanding chemical stability, SnO2 has been considered as a promising bifunctional material for supercapacitors as well as photocatalysts, but its poor conductivity and low surface area limit the specific capacitance and catalytic efficiency.

Insight into facet-dependent photocatalytic H2O2 production on BiOCl nanosheets

The generation of H₂O₂ on BiOCl(001) originates from O₂ reduction, while there are two pathways on BiOCl(010).

Measuring the Electrical and Photonic Properties of Cobalt Oxide-Containing Composite Carbon Fibers

In this work, cobalt acetate was incorporated into polyacrylonitrile (PAN) polymer through electrospinning as the cobalt oxide source. After oxidization and pyrolysis, a PAN-derived composite carbon fiber containing cobalt oxide was obtained. Measuring the electrical and photonic properties of the composite fiber under visible light irradiation was performed to evaluate the photoelectric behavior of the composite fiber. The p-type semiconducting behavior of the composite fiber was confirmed by measuring the open circuit voltage of a photochemical fuel cell consisting of the photosensitive electrode made from the composite fiber. The application of the composite fiber for glucose sensing was demonstrated.

Pd on poly(1-vinylimidazole) decorated magnetic S-doped grafitic carbon nitride: an efficient catalyst for catalytic reduction of organic dyes

A novel magnetic catalyst, (SGCN/Fe₃O₄/PVIs/Pd) was synthesized by growing of poly(1-vinylimidazole) on the surface of ionic liquid decorated magnetic S-doped graphitic carbon nitride, followed by stabilization of palladium nanoparticles. Catalytic activity of the prepared heterogeneous catalyst was explored for the catalytic reduction of hazardous dyes, methyl orange and Rhodamine B, in the presence of NaBH₄. Besides, the effects of the reaction variables on the catalytic activity were investigated in detail. The kinetics study established that dye reduction was the first order reaction and the apparent activation energy was calculated to be 72.63 kJ/mol and 68.35 kJ/mol¹ for methyl orange and Rhodamine B dyes, respectively. Moreover, ΔS^# and ΔH^# values for methyl orange were found to be − 33.67 J/mol K and 68.39 kJ/mol respectively. These values for Rhodamine B were − 45.62 J/mol K and 65.92 kJ/mol. The recycling test verified that the catalyst possessed good stability and reusability, thereby making it a good candidate for the catalytic purposes. Furthermore, a possible catalytic mechanism for dye catalytic reduction over SGCN/Fe₃O₄/PVIs/Pd was proposed.