Role of graphene on the surface chemical reactions of BiPO4-rGO with low OH-related defects

Boosting the sonophotocatalytic performance of BiOCl by Eu doping: DFT and an experimental study

Bismuth oxychloride (BiOCl) has a unique layered structure and uneven charge distribution, resulting in an internal electric field under polarization, which promotes the efficient separation and migration of photogenerated carriers. BiOCl could be a candidate for sonophotocatalysts. However, the low utilization of visible light limits the application of BiOCl in photocatalysts. In this study, the photocatalytic performance of rare earth element (Nd, Sm, Eu, Er and Er)-doped BiOCl was studied by density functional theory (DFT) and experimentally to screen high-performance catalysts. The band structure, density of states, and optical properties were calculated by the DFT method to predict the photocatalytic activity of rare earth-doped BiOCl. The built-in electric field formed in Eu-doped BiOCl inhibiting electron and hole recombination can be observed. Subsequently, the activity of the photocatalyst and sonophotocatalysts was evaluated. The results show that the photocatalytic and sonophotocatalytic activity of Eu-doped BiOCl is improved, which is consistent with the theoretical prediction. Combining theoretical calculations with experiments, the sonophotocatalytic activity of Eu-doped BiOCl is enhanced, mainly due to the synergistic effect of inhibiting carrier recombination, and expansion to the visible light absorption region.

Simultaneous Quantitation of Lead and Cadmium on an EDTA-Reduced Graphene Oxide-Modified Glassy Carbon Electrode

Cadmium (Cd) and lead (Pb) are classified as category one toxicants. The provisional guideline values, according to the World Health Organization (WHO), for Cd and Pb are 3 and 10 ppb, respectively. An easy, quick, and cheap analytical technique is in demand for the determination of these toxic heavy metals in water. Hence, a novel electrochemical sensing platform is developed by modifying the glassy carbon electrode with ethylenediaminetetraacetic acid (EDTA)-functionalized reduced graphene oxide (ErGO) for the low-cost simultaneous quantitation of toxic heavy-metal ions, lead and cadmium, in real water samples. EDTA is grafted to the surface of graphene oxide, via amine linkage, and the oxygen functionality is reduced by a green agent, tyrosine. Various physical and electrochemical characterizations of the as-prepared electrocatalytic material were performed by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), ζ-potential, ultraviolet diffuse reflectance spectroscopy (UV-DRS), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), etc. The glassy carbon electrode (GCE) is modified with ErGO by a simple drop-casting method for simultaneous metal-ion quantitation by differential pulse voltammetry (DPV). EDTA functionalization of graphene oxide and its further reduction using the green agent enhance the stability and sensitivity of the electrode substrate. The limits of detection for cadmium and lead ions calculated for ErGO/GCE are 1.02 and 2.52 ppb, while the limits of quantification for lead and cadmium ions are 3.41 and 8.4 ppb, and their sensitivities are 0.8 and 0.6 nA/ppb, respectively. Real river water contains 200.2 ± 0.38 ppb of Pb²⁺ ions (mean ± stdev, n = 3) by the DPV technique, which is validated by ICP-OES analysis.

Porous defective carbon ferrite for adsorption and photocatalysis toward nitrogen compounds in pre-treated biogas slurry

Carbon ferrite (C-Fe₃O₄) with hydrophilic functional groups and lattice defects was synthesized in anhydrous molten alkali system by fern leaves and ferric chloride as raw materials. Structural characterization results showed that carbon ferrite obtained oxygen-containing groups on the carbon surface. And structural pores and lattice defects resulted from spontaneous accumulation and “directive-connection” of ferrite (Fe₃O₄) nanoparticles. Carbon ferrite displayed an adsorption efficiency of 29.0% and excellent photocatalytic degradation of 80.8% toward nitrogen compounds (initial concentration of 430 mg/L) in pre-treated biogas slurry. The micromechanism for nitrogen compounds removal was discussed at the molecular/atomic level by exploring carbon ferrite “structure-activity”, which provides a design idea from microscopic perspective for the preparation of environmental materials with reactive sites.

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.

Tribocatalytic degradation of dyes by tungsten bronze ferroelectric Ba2.5Sr2.5Nb8Ta2O30 submicron particles

Searching for a new approach in environmental remediation in terms of dye degradation is important in industrialized society. In this work, ferroelectric Ba2.5Sr2.5Nb8Ta2O30 (BSNT) submicron powders prepared by the high-temperature solid-phase method are used for dye degradation under magnetic stirring. The dye in solution can be quickly degraded by magnetically stirring BSNT submicron particles in the dark in ambient temperature conditions. More importantly, the degradation efficiency can be greatly improved through simple modification of the stirring materials from glass to polypropylene, with a degradation efficiency of rhodamine B as high as 99% in 1.5 h at a gentle stirring speed of 300 rpm. Control experiments reveal that the degradation of the dye is mainly contributed by the friction between BSNT submicron particles and PTFE stirring rods. It is proposed that the friction between ferroelectric polar BSNT particles and PTFE causes charge transfer and induces a non-zero internal electric field to drive the separation of electron-hole pairs in BSNT particles, resulting in a novel tribocatalytic degradation of the dye, which is proven by the detection of ˙OH and ˙O2 - intermediate products during stirring. This work demonstrates that the friction energy of ferroelectric materials with strong polarization is an alternative approach for highly efficient dye degradation.

Enhanced active oxidative species generation over Fe-doped defective TiO2 nanosheets for boosted photodegradation

Semiconductor photocatalysis is widely proposed for decomposing multiple pollutants via photo-generated oxidative species. However, the photocatalytic degradation performance in practical settings still remains unsatisfactory due to the limited production of active oxidative species (AOS). In this work, a defect engineering strategy was developed to explore the superiority of oxygen vacancies (Vo) and their structural regulation to enhance AOS production for boosting photodegradation. Taking anatase TiO₂ as a model photocatalyst, ultrathin TiO₂ nanosheets containing abundant Vo and appropriate Fe doping exhibited an unprecedented 134 times higher activity in the degradation of Rhodamine B (RhB) (rate as high as 0.3073 min⁻¹) than bulk anatase and were superior to most reported photocatalysts. The defect-rich ultrathin TiO₂ nanosheets could be further applied in high-efficiency degradation of tetracycline hydrochloride (TC-HCl) with the degradation rate of 0.0423 min⁻¹. The in situ electron paramagnetic resonance, advanced spectroscopic characterization and electrochemical measurement revealed the key role of Vo and Fe doping in facilitating the production of photo-generated holes and superoxide radicals (˙O₂⁻) that were identified to be effective to decompose both RhB and TC-HCl. This research provides insight into defect engineering promoting AOS generation and gives inspiration for the design of efficient photocatalysts for photooxidation applications.

Defect-rich ultrathin TiO₂ nanosheets with tunable Fe doping realize the efficient generation of active oxidative species for boosted dye/antibiotic photodegradation.

High-efficient synergy of piezocatalysis and photocatalysis in bismuth oxychloride nanomaterial for dye decomposition

In this work, it is found that the hydrothermally-synthesized bismuth oxychloride can behave both the piezocatalysis and photocatalysis for the Rhodamine B dye decomposition. ∼99% decomposition efficiency is achieved after both vibrating and lighting the Rhodamine B dye solution for ∼96 min with the addition of bismuth oxychloride catalyst, while the ∼72% and ∼26% decomposition efficiencies are obtained for only photocatalysis or only piezocatalysis respectively. In bi-catalysis, the mechanical strain produced due to vibration will directly provide an electric field that will increase the separation between the photo-induced electron-hole pairs, yielding to the enhanced decomposition performance of bi-catalysis. There is no significant change in the bi-catalytic performance of bismuth oxychloride nanomaterial observed after being recycled four times. Bismuth oxychloride catalyst is potential for the bi-catalytic decomposition treatment of wastewater through harvesting both the environmental vibration energy and light energy.

Construction of 2D heterojunction system with enhanced photocatalytic performance: Plasmonic Bi and reduced graphene oxide co-modified Bi5O7I with high-speed charge transfer channels

The efficient electron-hole charge pair separation, ultra-fast electron migration and excellent light harvest capacity are essential for semiconductor photocatalyst with superior photocatalytic performance. In this study, we constructed layered 2D/2D heterojunction composite of Bi@Bi₅O₇I/rGO (BiBGOI) through a facile surface charge mediated self-assembly strategy. The unique 2D/2D heterostructure with face to face contact can increase the contact area and generate a large amount of charge transfer nanochannels in the interfacial heterojunction, resulting in the enhancement of photocatalytic activity. Addition of semimetal Bi can enhance light absorption, and the local electromagnetic field dominated by SPR effect is favorable for photoinduced charge pair separation. The novel composite showed superior photocatalytic performance for decomposing levofloxacin (LVFX), which was attributed to the unique 2D/2D structure and SPR effect. The enhanced mineralization ability of the novel composite was ascribed to the strong oxidization ability of photoinduced holes, further evaluating high charge pair separation efficiency. In addition, the strong adsorption capacity of rGO for LVFX molecules can enable active radicals transfer into the surface to decompose it. This work will shed light on constructing 2D/2D heterojunction system assisted with SPR effect for the practical application in removal of organic pollutants.

Structures and energetics of low-index stoichiometric BiPO4surfaces

Four low-index surfaces of monazite BiPO₄in the Wulff shape are investigated.

Photothermally Enabled Pyro-Catalysis of a BaTiO3 Nanoparticle Composite Membrane at the Liquid/Air Interface

This paper reports the highly efficient pyroelectric nanomaterial-based catalytic degradation of waste dye under rapid temperature oscillation, which was achieved by periodical solar irradiation on a porous pyroelectric membrane that was floating at the liquid/air interface. Such a membrane consists of the light-to-heat conversion carbon black film as the top layer and the porous poly(vinylidene difluoride) (PVDF) film embedded with pyroelectric barium titanate (BaTiO₃) nanoparticles (BTO NPs) as the bottom layer. By using an optical chopper, solar light can be modulated to periodically irradiate on the floating membrane. Because of the photothermal effect and low thermal conductivity of the PVDF polymer, the generated heat is localized at the surface of the membrane and substantially increases the surface temperature within a short period of time. When the solar light is blocked by the chopper, interfacial evaporation through the porous membrane along with convective air cooling and radiative cooling leads to heat dissipation, and then the temperature of the membrane is rapidly decreased. Such an efficient thermal cycle results in a substantial rate of temperature change of the membrane, which enhances its pyroelectric capability and subsequent pyro-catalysis. In contrast, the efficiency of pyro-catalysis through the dispersed BTO NP solution is about 4 times lower than that of the BTO composite membrane. With the large heat capacity of the aqueous solution and inevitable thermal loss because of bulk heating, the rate of temperature change of the BTO NP solution is much smaller than that of the BTO composite membrane and thus results in a relatively small pyro-catalytic capability. Furthermore, the reusability and transferability of this newly developed composite membrane make it amenable to practical use in treating contaminated water. The findings in our report not only offer a new design strategy for efficient solar-enabled pyro-catalysis but also pave a new way to rationally harvest solar-thermal energy in nature for various applications that involve pyroelectric materials.

Highly efficient pyrocatalysis of pyroelectric NaNbO3 shape-controllable nanoparticles for room-temperature dye decomposition

In this work, pyrocatalytic effect is realized in hydrothermally-synthesized pyroelectric NaNbO₃ shape-controllable nanoparticles via the product of pyroelectric effect and electrochemical redox. A pyro-catalysis is designed to decompose dye wastewater. Under the 23-50 °C heating-cooling cycle, the maximum pyrocatalytic decomposition ratio of NaNbO₃ nanorods, nanosheets and nanocubes are 96%, 76% and 33%, respectively. The pyrocatalytic effect of NaNbO₃ nanoparticles is potential in developing a environmentally-friendly technology for room-temperature pyrocatalysis through utilizing natural heat energy.

Facile one-pot synthesis of visible light-responsive BiPO4/nitrogen doped graphene hydrogel for fabricating label-free photoelectrochemical tetracycline aptasensor

It is fundamental to develop highly efficient visible light-responsive photoelectrochemical (PEC) performance material for fabricating PEC biosensor. Herein, BiPO₄/three-dimensional nitrogen doped graphene hydrogel (3DNGH) nanocomposites were prepared for the first time via a facile one-pot hydrothermal route. In this nanoarchitecture, the BiPO₄ nanorods were anchored onto the porous structure of 3DNGH. Compared with pristine BiPO₄, the absorption of BiPO₄/3DNGH has been extend to visible-light region, and the energy band gap of BiPO₄/3DNGH was calculated to be 2.10 eV, which was greatly narrower than that of pristine BiPO₄ with a band gap of 3.85 eV. Under visible light irradiation, the photocurrent signal of the as-prepared BiPO₄/3DNGH was 847.2-fold, 4.1-fold and 2.3-fold enhanced comparing to pristine BiPO₄, BiPO₄ functionalized reduced graphene oxide and BiPO₄/nitrogen doped graphene. The enhancement of such photocurrent signal was attributed to the introduction of 3DNGH, which was capable to improve the charge transfer rate and also the efficiency of visible-light utilization of BiPO₄. Based on the excellent PEC properties of BiPO₄/3DNGH, a label-free PEC aptasensor for selectivity and sensitivity detection of tetracycline (Tc) was successfully established by using Tc aptamer as a biorecognition element. Under optimized conditions, the proposed PEC aptasensor exhibited a wide linear in the range from 0.1 nmol L^-1 to 1 μmol L^-1 as well as a low detection limit of 0.033 nmol L^-1 (S/N = 3). The prepared BiPO₄/3DNGH nanocomposites would serve as a promising visible light-responsive photoactive material for fabrication of PEC biosensors with high performance.

Oxygen Reduction Reaction for Generating H2 O2 through a Piezo-Catalytic Process over Bismuth Oxychloride

Oxygen reduction reaction (ORR) for generating H₂ O₂ through green pathways have gained much attention in recent years. Herein, we introduce a piezo-catalytic approach to obtain H₂ O₂ over bismuth oxychloride (BiOCl) through an ORR pathway. The piezoelectric response of BiOCl was directly characterized by piezoresponse force microscopy (PFM). The BiOCl exhibits efficient catalytic performance for generating H₂ O₂ (28 μmol h^-1 ) only from O₂ and H₂ O, which is above the average level of H₂ O₂ produced by solar-to-chemical processes. A piezo-catalytic mechanism was proposed: with ultrasonic waves, an alternating electric field will be generated over BiOCl, which can drive charge carriers (electrons) to interact with O₂ and H₂ O, then to form H₂ O₂ .

Efficient interfacial charge transfer through plasmon sensitized Ag@Bi2O3 hierarchical photoanodes for photoelectrocatalytic degradation of chlorinated phenols

Understanding the interfacial charge transfer behavior of plasmonically active Ag decorated hierarchical Bi₂O₃ photoanodes for the photo-electro-oxidation of chlorinated phenols.

Defect-mediated electron–hole separation in semiconductor photocatalysis

This review summarizes the inherent functionality of bulk, surface and interface defects, and their contributions towards mediating electron–hole separation in semiconductor photocatalysis.

Photo-reduction of bromate in drinking water by metallic Ag and reduced graphene oxide (RGO) jointly modified BiVO4 under visible light irradiation

Bromate (BrO3(-)), an oxyhalide disinfection by-product (DBP) in drinking water, has been demonstrated to be carcinogenic and genotoxic. In the current work, metallic Ag and reduced graphene oxide (RGO) co-modified BiVO4 was successfully synthesized by a stepwise chemical method coupling with a photo-deposition process and applied in the photo-reduction of BrO3(-) under visible light irradiation. In this composite, metallic Ag acted as an electron donor or mediator and RGO enhanced the BrO3(-) adsorption onto the surface of catalysts as well as an electron acceptor to restrict the recombination of photo-generated electron-hole pairs. The Ag@BiVO4@RGO composite exhibited greater photo-reduction BrO3(-) performance than pure BiVO4, Ag@BiVO4 and RGO@BiVO4 under identical experimental conditions: initial BrO3(-) concentration 150 μg/L, catalyst dosage 0.5 g/L, pH 7.0 and visible light (λ > 420 nm). The photoluminescence spectra (PL), electron-spin resonance (ESR), photocurrent density (PC) and electrochemical impedance spectroscopy (EIS) measurements indicated that the modified BiVO4 enhanced the photo-generated electrons and separated the electron-hole pairs. The photocatalytic reduction efficiency for BrO3(-) removal decreased with the addition of electron quencher K2S2O8, suggesting that electrons were the primary factor in this photo-reduction process. The declining photo-reduction efficiency of BrO3(-) in tap water should attribute to the consumption of photo-generated electrons by coexisting anions and the adsorption of dissolved organic matter (DOM) on graphene surface. The overall results indicate a promising application potential for photo-reduction in the DBPs removal from drinking water.

Strong pyro-catalysis of pyroelectric BiFeO3 nanoparticles under a room-temperature cold-hot alternation

A strong pyro-catalytic dye degradation with an ultrahigh degradation efficiency (>99%) in hydrothermally synthesized pyroelectric BiFeO3 nanoparticles was achieved under a room-temperature cold-hot alternating excitation (between 27 °C to 38 °C). The pyro-catalysis originated from a combination of the pyroelectric effect and the electrochemical oxidation-reduction reaction. The intermediate products (hydroxyl radicals and superoxide radicals) of pyro-electro-catalysis were observed. Pyro-catalysis provides a highly efficient and reusable dye wastewater decomposition technology through utilizing environmental day-night temperature variation.

An investigation into the solar light-driven enhanced photocatalytic properties of a graphene oxide–SnO2–TiO2ternary nanocomposite

Highly efficient graphene oxide–SnO₂–TiO₂ternary nanocomposite was designedviaone step solvothermal method considering the step-wise band edge energy levels of each component and the corresponding photocatalytic performance was investigated.

A review of BiPO4, a highly efficient oxyacid-type photocatalyst, used for environmental applications

This review presents the recent progress on the oxyacid-type photocatalyst, BiPO₄, which possesses excellent UV-activity for environmental applications.

A nanosheet-like BiPO4/Bi2O2CO3 heterostructured photocatalyst with enhanced photocatalytic activity

The as-formed BiPO₄/Bi₂O₂CO₃ heterojunction structure can facilitate interfacial charge transfer, thereby resulting in enhanced photocatalytic activity.

AgBr nanoparticles decorated BiPO4 microrod: a novel p–n heterojunction with enhanced photocatalytic activities

AgBr nanoparticles were decorated on the surface of BiPO₄ micro-rod to fabricate a novel p–n heterojunction photocatalyst via a facile deposition–precipitation method.

Graphene-analogue boron nitride/Ag3PO4 composite for efficient visible-light-driven photocatalysis

Graphene-analogue BN modified Ag₃PO₄ photocatalysts were successfully prepared. In the presence of the BN, it could effectively enhance the photoactivity and stability of Ag₃PO₄.

Photoelectrocatalytic degradation of rhodamine B on TiO2 photonic crystals

The possible degradation mechanisms of TiO₂ photonic crystals in photoelectrocatalytic and photocatalytic systems were compared and put forward.

Ionic liquid-assisted hydrothermal synthesis of Bi2WO6–reduced graphene oxide composites with enhanced photocatalytic activity

Due to the synergistic contributions of graphene and ionic liquid, the as-prepared RGO–Bi₂WO₆ samples exhibited the remarkably enhanced photocatalytic activities under visible light irradiation.