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Journal articleJiamprasertboon A, Kafizas A, Eknapakul T, et al., 2025,
Insights into unlocking the latent photocatalytic H2 production activity in the protonated Aurivillius-phase layered perovskite Na0.5Bi2.5Nb2O9
, Materials Research Bulletin, Vol: 186, ISSN: 0025-5408The introduction of protonated interlayers in layered perovskite compounds has already demonstrated promising results in terms of photocatalytic activity. However, the mechanisms behind the observed enhancements remain unexplored. Here, we report a rapid and efficient proton exchange process for Na0.5Bi2.5Nb2O9 (ABNO), involving selective leaching of (Bi2O2)2- layers accompanied by the introduction of interlayer H+. This process, using acid treatment at room temperature is completed within only 24 h, the fastest method to date for a layered perovskite. Protonation induces changes at the molecular and electronic level, investigated using Synchrotron-based techniques, diffused reflectance spectroscopy (DRS), DFT calculation, and transient absorption spectroscopy (TAS), influencing the electronic band structure, surface properties, and charge carrier dynamics of the compounds. After protonation, BET surface area increases by > 20 times, to 156.19 m2/g. These structural and surface modifications unlock the material's latent photocatalytic potential, enabling H+ exchanged Na0.5Bi2.5Nb2O9 (HABNO) to achieve a H2 production rate of 242 μmol/h/g. This work delves into the photocatalytic mechanism, revealing how substitution by H+ provides more active sites and enhances the ability of the material to generate more highly reactive electrons that can participate in H2O reduction. This study highlights the promising strategy of altering the structure and electronic properties of layered materials through protonation to improve their performance for applications in photocatalysis for a cleaner and more sustainable future.
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Journal articleOlaifa O, Alimard P, Itskou I, et al., 2025,
Purifying the Air with Photocatalysis: Developing Bismuth Oxybromide/ Copper Phthalocyanine Composite Photocatalyst Filters with Enhanced Activity for NO<sub>x</sub> Removal
, ChemPhotoChem, ISSN: 2367-0932<jats:title>Abstract</jats:title><jats:p>The utilization of photocatalysis is a promising new strategy for reducing the substantially high levels of nitrogen oxides (NO<jats:sub>x</jats:sub>) pollution in cities. In this work, we examine bismuth oxybromide (BiOBr) as a viable substitute due to its narrower band gap and high stability. Powders were synthesised using co‐precipitation, solvothermal and hydrothermal synthesis methods, resulting in particles with various morphologies including microcubes, microspheres, microflowers, clusters and microsquares. Their photocatalytic activities being evaluated in accordance with ISO 22197–1 : 2016 protocol under UV and visible light. The samples exhibiting the highest performance were produced by co‐precipitation, showing ~7 % NO and ~2 % NO<jats:sub>x</jats:sub> removal under visible light and ~19 % NO and ~10 % NO<jats:sub>x</jats:sub> removal under UV light. The activity was further enhanced, by incorporating copper(II) phthalocyanine (CuPc) through an impregnation method, where the optimal loading of 0.01 mol% surpassed the activity of the benchmark photocatalyst TiO<jats:sub>2</jats:sub> P25, with ~22 % NO and ~9 % NO<jats:sub>x</jats:sub> removal under visible light and ~40 % NO and ~23 % NO<jats:sub>x</jats:sub> under UV light. We anticipate that these BiOBr/CuPc photocatalyst filters can be applied within air purification systems and powered using less energy intensive visible light sources to remedy air pollution.</jats:p>
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Journal articleTam B, Pike SD, Nelson J, et al., 2025,
The scalable growth of high-performance nanostructured heterojunction photoanodes for applications in tandem photoelectrochemical-photovoltaic solar water splitting devices.
, Chem Sci, ISSN: 2041-6520Due to their complementary absorption characteristics and band energy structure, the BiVO4-coated WO3 heterojunction architecture is commonly employed as a metal oxide photoanode for the water oxidation half-reaction. The energy level ordering results in a staggered heterojunction that can effectively separate photoexcited electrons into the WO3 layer towards the current collector and photoexcited holes into the BiVO4 layer towards the interface with the electrolyte. Chemical vapour deposition (CVD) is an upscalable technique for fabricating large-area thin films of a wide range of semiconductors with nanoscale control. The fluorine-doped tin oxide (FTO)-coated transparent conductive glass substrates used herein are mass-produced by the glass industry with atmospheric pressure CVD and so the entire photoelectrode could be produced in one production process on float glass panels. This work is a detailed study of the use of atmospheric pressure CVD to fully-fabricate high-performance BiVO4-coated WO3 nanostructures (500-2000 nm in length with 25-100 nm thick BiVO4 coatings) for photoelectrochemical (PEC) water splitting. Incident photon-to-current efficiency measurements were used to calculate optimal solar predicted photocurrents of 1.92 and 2.61 mA cm-2 (2.3% and 3.2% solar-to-hydrogen efficiency if coupled to a hypothetical photovoltaic providing 1.23 V) for WO3/BiVO4 heterojunction samples under front and back-illumination, respectively. The heterojunction showed more than additive improvements over the parent materials, with bare WO3 and BiVO4 samples showing 0.68 and 0.27 mA cm-2 and 0.50 and 0.87 mA cm-2 under front and back-illumination, respectively. Simulations of the current-voltage characteristics of tandem crystalline silicon photovoltaic modules coupled to the PEC devices were consistent with the solar predicted photocurrents. These promising results for BiVO4-coated WO3 nanoneedles fully-deposited by atmospheric pressure CVD enables future research into
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Journal articleCreasey GH, McCallum TW, Ai G, et al., 2025,
Mechanically and photoelectrochemically stable WO<inf>3</inf>
, Journal of Materials Chemistry A, ISSN: 2050-7488The development of scalable, stable and high performance photoelectrodes remains the major bottleneck in up-scaling photoelectrochemical (PEC) water splitting systems. A photoanode structure of particular promise is WO3|BiVO4, where the formation of staggered heterojunction between nanostructured WO3 and a thin layer of BiVO4 mitigates charge carrier mobility limitations present for BiVO4 alone and suppresses recombination. Although these electrodes remain prone to photo-corrosion, this effect can be mitigated through the application of water oxidation surface co-catalysts. An additional challenge that has rarely been addressed in the literature to date is the need for strong adhesion to the substrate and mechanical stability of these photoelectrodes, so that they can withstand flow-induced shear stress exerted by the electrolyte in continuous flow under operational conditions. Herein, we propose a scalable route to synthesising WO3|BiVO4|NiFeOOH photoanodes entirely by aerosol-assisted chemical vapour deposition (AA-CVD). The mechanical stability of the WO3|BiVO4 heterojunction was optimised by tuning the morphology of the WO3 underlayer and improving its adhesion to the FTO transparent substrate. To address BiVO4 dissolution at the electrode|electrolyte interface, we fabricated a NiFeOOH co-catalyst by a novel AA-CVD method. This suppressed BiVO4 dissolution and enhanced the water oxidation performance of the photoanode, characterised by linear sweep voltammetry (LSV), photoelectrochemical impedance spectroscopy (PEIS) and chopped chronoamperometry. The photoanode materials were physically characterised by X-ray diffraction (XRD), UV-Vis spectroscopy, scanning electron microscopy (SEM), high resolution transmission electron microscopy (HR-TEM), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and time-of-flight secondary ion mass spectrometry (ToF-SIMS). Our optimised photoanodes with 1 cm2 photoactive area delivered a stable photocurrent density of 1.75
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Journal articleHeiba HF, Bullen JC, Kafizas A, et al., 2024,
Engineered Sn-TiO2@SnO2 and SnO2@Sn-TiO2 heterophotocatalysts for enhanced As(III) remediation: a comprehensive bulk and surface characterization and precise photocatalytic oxidation rates determination
, Colloids and Surfaces A: Physicochemical and Engineering Aspects, Vol: 702, ISSN: 0927-7757Arsenite, As(III), is a highly toxic form of arsenic that poses a significant risk to human health if present in drinking water. Oxidation of As(III) to the less toxic As(V) using TiO2 as photocatalyst is an attractive solution in water treatment applications but challenged the high bandgap energy. In this study, we investigate the potential of doping TiO2 with Sn to reduce the bandgap and hence to improve the photocatalytic oxidation (PCO). To this end, we studied first the effect of varying Sn:TiO2 molar doping on the structure of the newly synthesized SnO2@TiO2 and Sn-TiO2@SnO2 hetero photocatalysts. We found that at low Sn:TiO2 doping ratios (0.1Sn:1TiO2), SnO2 tends to float on the surface and form a coat around the TiO2 (SnO2@Sn-TiO2), whereas at higher doping ratio (1Sn:1TiO2) a Sn-TiO2 coat forms alongside SnO2 clusters in the core of the catalyst (Sn-TiO2@SnO2). We assessed the PCO and observed significant shifts to lower conduction and valence band edge energies and a reduction of the bandgap at higher doping ratios. The smallest bandgap was 2.87 eV with a doping ratio of 1Sn:1TiO2. Sn-TiO2@SnO2 and as SnO2@Sn-TiO2 improved the PCO of TiO2 by ∼30 and 46 %, respectively. We finally determined the rate constant (k) for the As(III) oxidation using a combination of spectrochemical and surface sensitive techniques and determined for a 1Sn:1TiO2 (i.e. Sn-TiO2@SnO2) catalyst a value of 0.055 ±0.002 min−1, i.e., 78 folds faster than using only TiO2. We conclude that Sn doping of TiO2 is a very promising approach for improving the PCO of As(III) in water treatment.
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Journal articleHeiba HF, Bullen JC, Kafizas A, et al., 2024,
Role of the Sn-TiO<sub>2</sub>/Ti-SnO<sub>2</sub> Heterojunction in Enhancing the Photocatalytic Oxidation of Arsenite (As<SUP>III</SUP>) through the Promotion of Charge Carrier Lifetime
, ACS APPLIED MATERIALS & INTERFACES, Vol: 16, Pages: 69239-69252, ISSN: 1944-8244 -
Journal articleDutta A, Porat H, Goldreich A, et al., 2024,
Laser exfoliated 2D MXene for supercapacitor applications
, CHEMICAL ENGINEERING JOURNAL, Vol: 500, ISSN: 1385-8947 -
Journal articleAlimard P, Gong C, Itskou I, et al., 2024,
Achieving high photocatalytic NOx removal activity using a Bi/BiOBr/TiO2 composite photocatalyst
, Chemosphere, Vol: 368, ISSN: 0045-6535Fossil fuel combustion generates nitrogen oxides (NO + NO2 = NOx), which pose threats to the environment and human health. Although commercial products containing titanium dioxide (TiO2) can remedy NOx pollution by photocatalysis, they only function in the ultraviolet (UV). On the other hand, bismuth oxybromide (BiOBr) is active in the visible. BiOBr is stable, affordable, and non-toxic, making it an appealing alternative. In addition, nanoparticulate Bi metal can further enhance visible light absorption through its surface plasmon properties and charge carrier lifetime by spatially separating charge. In this study, to enhance the visible-light activity of TiO2-based photocatalysts for NOx pollution, a composite of Bi-decorated BiOBr/TiO2 was synthesised using a solvothermal method across varying the Ti/Bi atomic ratio (0.2, 2.2, 4.4, and 6.6), and synthesis duration (6h, 12h, and 18h). The photocatalytic performance of the synthesised composites for NO gas removal was investigated using an adapted ISO method (22197–1:2016). Analysis showed that the preferential growth of the (010) crystal facet in BiOBr and the presence of Bi metal both play an important role in the superior photocatalytic activity seen in our Bi-decorated BiOBr/TiO2 composite. The composites were characterised using X-ray diffraction (XRD), attenuated total reflectance - Fourier transform infrared spectroscopy (ATR-FTIR), high-resolution scanning electron microscopy (HR-SEM), UV–Vis diffuse reflectance (DRS) spectroscopy, transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, Brunauer-Emmett-Teller (BET) analysis, thermogravimetric analysis (TGA), and diffuse reflectance transient absorption spectroscopy (DR-TAS). Our research shows that the Bi/BiOBr–TiO2 composite synthesised through a 12h solvothermal meth
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Journal articleZhao S, Jia C, Shen X, et al., 2024,
The aerosol-assisted chemical vapour deposition of Mo-doped BiVO4 photoanodes for solar water splitting: an experimental and computational study
, Journal of Materials Chemistry A, Vol: 12, Pages: 26645-26666, ISSN: 2050-7488BiVO4 is one of the most promising light absorbing materials for use in photoelectrochemical (PEC) water splitting devices. Although intrinsic BiVO4 suffers from poor charge carrier mobility, this can be overcome by Mo-doping. However, for Mo-doped BiVO4 to be applied in commercial PEC water splitting devices, scalable routes to high performance materials need to be developed. Herein, we propose a scalable aerosol-assisted chemical vapour deposition (AA-CVD) route to high performance Mo-doped BiVO4. The materials were characterised using X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), atomic force microscopy (AFM), UV-visible absorption spectroscopy, and a range of PEC tests. By studying a range of Mo-precursor doping levels (0 to 12% Mo : V), an optimum precursor doping level was found (6% Mo : V); substituting V5+ sites in the host structure as Mo6+. In PEC water oxidation the highest performing material showed an onset of photocurrent (Jon) at ∼0.6 VRHE and a theoretical solar photocurrent (TSP) of ∼1.79 mA cm−2 at 1.23 VRHE and 1 sun irradiance. Importantly, Mo-doping was found to induce a phase change from monoclinic clinobisvanite (m-BiVO4), found in undoped BiVO4, to tetragonal scheelite (t-BiVO4). The effect of Mo-doping on the phase stability, structural and electronic properties was examined with all-electron hybrid exchange density functional theory (DFT) calculations. Doping into V and Bi sites at 6.25 and 12.5 at% was calculated for t-BiVO4 and m-BiVO4 phases. In accord with our observations, 6.25 at% Mo doping into the V sites in t-BiVO4 is found to be energetically favoured over doping into m-BiVO4 (by 2.33 meV per Mo atom inserted). The computed charge density is consistent with n-doping of the lattice as Mo6+ replaces V5+ generating an occupied mid-gap state ∼0.4 eV below the conduction band minimum (CBM) which is primarily of Mo-4d character. Doubling this do
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Journal articleItskou I, Kafizas A, Nevjestic I, et al., 2024,
Effects of phosphorus doping on amorphous boron nitride’s chemical, sorptive, optoelectronic, and photocatalytic properties
, The Journal of Physical Chemistry C, Vol: 128, Pages: 13249-13263, ISSN: 1932-7447Amorphous porous boron nitride (BN) represents a versatile material platform with potential applications in adsorptive molecular separations and gas storage, as well as heterogeneous and photo-catalysis. Chemical doping can help tailor BN’s sorptive, optoelectronic, and catalytic properties, eventually boosting its application performance. Phosphorus (P) represents an attractive dopant for amorphous BN as its electronic structure would allow the element to be incorporated into BN’s structure, thereby impacting its adsorptive, optoelectronic, and catalytic activity properties, as a few studies suggest. Yet, a fundamental understanding is missing around the chemical environment(s) of P in P-doped BN, the effect of P-doping on the material features, and how doping varies with the synthesis route. Such a knowledge gap impedes the rational design of P-doped porous BN. Herein, we detail a strategy for the successful doping of P in BN (P-BN) using two different sources: phosphoric acid and an ionic liquid. We characterized the samples using analytical and spectroscopic tools and tested them for CO2 adsorption and photoreduction. Overall, we show that P forms P–N bonds in BN akin to those in phosphazene. P-doping introduces further chemical/structural defects in BN’s structure, and hence more/more populated midgap states. The selection of P source affects the chemical, adsorptive, and optoelectronic properties, with phosphoric acid being the best option as it reacts more easily with the other precursors and does not contain C, hence leading to fewer reactions and C impurities. P-doping increases the ultramicropore volume and therefore CO2 uptake. It significantly shifts the optical absorption of BN into the visible and increases the charge carrier lifetimes. However, to ensure that these charges remain reactive toward CO2 photoreduction, additional materials modification strategies should be explored in future work. These strategies could include the
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Journal articleJeong SB, Heo KJ, Yoo JH, et al., 2024,
Photobiocidal activity of TiO2/UHMWPE composite activated by reduced graphene oxide under white light
, Nano Letters: a journal dedicated to nanoscience and nanotechnology, Vol: 24, Pages: 9155-9162, ISSN: 1530-6984Herein, we introduce a photobiocidal surface activated by white light. The photobiocidal surface was produced through thermocompressing a mixture of titanium dioxide (TiO2), ultra-high-molecular-weight polyethylene (UHMWPE), and reduced graphene oxide (rGO) powders. A photobiocidal activity was not observed on UHMWPE-TiO2. However, UHMWPE-TiO2@rGO exhibited potent photobiocidal activity (>3-log reduction) against Staphylococcus epidermidis and Escherichia coli bacteria after a 12 h exposure to white light. The activity was even more potent against the phage phi 6 virus, a SARS-CoV-2 surrogate, with a >5-log reduction after 6 h exposure to white light. Our mechanistic studies showed that the UHMWPE-TiO2@rGO was activated only by UV light, which accounts for 0.31% of the light emitted by the white LED lamp, producing reactive oxygen species that are lethal to microbes. This indicates that adding rGO to UHMWPE-TiO2 triggered intense photobiocidal activity even at shallow UV flux levels.
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Journal articleReddick C, Sotelo-Vazquez C, Tam B, et al., 2024,
Photoelectrochemical disinfection efficiency of WO3-based photoanodes: development of multifunctional photoelectrocatalytic materials
, Catalysis Today, Vol: 437, ISSN: 0920-5861Access to safe water is a growing global concern, with millions lacking acceptable water sources. Photocatalysis offers eco-friendly water remediation, yet its combination with electrocatalysis for both water treatment and hydrogen production remain underexplored. This study investigates UVA LED photoelectrocatalysis using WO3-based photoanodes, alone or in heterojunction with BiVO4, to purify wastewater and co-produce hydrogen. Tests on polluted water streams containing 105 PFU mL−1 of MS2 bacteriophage virus and 106 CFU mL−1 of E. coli reveal that nanostructured WO3 achieves rapid MS2 disinfection within 5 min. (k= 0.80 min−1), with enhanced efficiency over flat counterparts. However, nanostructuring does not improve E. coli inactivation due to bacterium size constraints. These findings advance the design of tandem photoreactors for dual wastewater purification and energy generation.
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Journal articleLin Z-P, Li Y, Haque SA, et al., 2024,
Insights from experiment and machine learning for enhanced TiO₂ coated glazing for photocatalytic NOₓ remediation
, Journal of Materials Chemistry A, Vol: 12, Pages: 13281-13298, ISSN: 2050-7488In this study, 58 distinct TiO2-coated glass samples were synthesized via Atmospheric Pressure Chemical Vapour Deposition (APCVD) under controlled synthesis conditions. The crystal properties, optical properties, surface properties and photogenerated charge carrier behaviour of all synthesized samples were characterized by X-ray diffraction (XRD), UV-visible spectroscopy, atomic force microscopy (AFM), and transient absorption spectroscopy (TAS), respectively. The photocatalytic activity of all coatings was systematically assessed against NO gas under near-ISO (22 197-1:2016) test conditions. The most active TiO2 coating showed ∼22.3% and ∼6.6% photocatalytic NO and NOx conversion efficiency, respectively, with this being ∼60 times higher than that of a commercial self-cleaning glass. In addition, we compared the accuracy of different machine learning strategies in predicting photocatalytic oxidation performance based on experimental data. The errors of the best strategy for predicting NO and NOx removal efficiency on the entire data set were ±2.20% and ±0.92%, respectively. The optimal ML strategy revealed that the most influential factors affecting NO photocatalytic efficiency are the sample surface area and photogenerated charge carrier lifetime. We then successfully validated our ML predictions by synthesising a new, high-performance TiO2-coated glass sample in accordance with our ML simulated data. This sample performed better than commercially available self-cleaning glass under a new metric, which comprehensively considered the visible light transmittance (VLT), NO degradation rate and NO2 selectivity of the material. Not only did this research provide a panoramic view of the links between synthesis parameters, physical properties, and NOx removal performance for TiO2-coated glass, but also showed how ML strategies can guide the future design and production of more effective photocatalytic coatings.
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Journal articleTam B, Babacan O, Kafizas A, et al., 2024,
Comparing the net-energy balance of standalone photovoltaic-coupled electrolysis and photoelectrochemical hydrogen production
, Energy and Environmental Science, Vol: 17, Pages: 1677-1694, ISSN: 1754-5692Photovoltaic-coupled electrolysis (PV-E) and photoelectrochemical (PEC) water splitting are two options for storing solar energy as hydrogen. Understanding the requirements for achieving a positive energy balance over the lifetime of facilities using these technologies is important for ensuring sustainability. While neither technology has yet reached full commercialisation, they are also at very different technology readiness levels and scales of development. Here, we model the energy balance of standalone large-scale facilities to evaluate their energy return on energy invested (ERoEI) over time and energy payback time (EPBT). We find that for average input parameters based on present commercialised modules, a PV-E facility shows an EPBT of 6.2 years and ERoEI after 20 years of 2.1, which rises to approximately 3.7 with an EPBT of 2.7 years for favourable parameters using the best metrics amongst large-scale modules. The energy balance of PV-E facilities is influenced most strongly by the upfront embodied energy costs of the photovoltaic component. In contrast, the simulated ERoEI for a PEC facility made with earth abundant materials only peaks at 0.42 after 11 years and about 0.71 after 20 years for facilities with higher-performance active materials. Doubling the conversion efficiency to 10% and halving the degradation rate to 2% for a 10-year device lifetime can allow PEC facilities to achieve an ERoEI after 20 years of 2.1 for optimistic future parameters. We also estimate that recycling the materials used in hydrogen production technologies improves the energy balance by 28% and 14% for favourable-case PV-E and PEC water splitting facilities, respectively.
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Journal articleYang G, Zhou Y, Wang M, et al., 2023,
Elucidating the effect of nitrogen occupancy on the hydrogen evolution reaction for a series of titanium oxynitride electrocatalysts
, ChemCatChem, Vol: 15, ISSN: 1867-3880Titanium nitride (TiN) shows desirable properties for use as an electrocatalyst and catalyst support, as it possesses high electrical conductivity and excellent corrosion resistance. Any oxygen and humidity present or incomplete nitridation during the synthesis process of nitrides can lead to an increasing oxygen content. However, the role of oxygen contents or nitrogen occupancies in the bulk of the nitrides during the electrocatalytic reactions is not well understood. In this work, we have synthesised a series of titanium oxynitrides with varied bulk nitrogen occupancies by ammonolysis at different temperatures. Higher ammonolysis temperatures will give a higher nitrogen occupancy but result in a lower surface area. The geometric activities towards the hydrogen evolution reaction (HER) have been normalised by the electrochemically active surface areas (ECSA) and the BET surface areas to get the specific activities. Their specific activity towards the HER is found to be strongly correlated with the bulk nitrogen occupancy and a higher bulk nitrogen occupancy is beneficial to the specific HER activities.
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Journal articleWilson AA, Shalvey TP, Kafizas A, et al., 2023,
Analysis of charge trapping and long lived hole generation in SrTiO<sub>3</sub> photoanodes
, SUSTAINABLE ENERGY & FUELS, Vol: 7, Pages: 5066-5075, ISSN: 2398-4902Charge carrier dynamics studies of SrTiO3 under applied bias offer the opportunity to gain unique insights into what underpins its state-of-the-art photocatalytic water splitting activity. Herein, time resolved spectroscopic measurements are employed, to investigate the impact of applied bias on the transient and steady state charge carrier dynamics of SrTiO3 across μs–s timescales, and simultaneously measure charge extraction kinetics. A high density of Ti3+ defect states in SrTiO3 photoanodes are identified and associated with prevalent electron trapping into deep states, which is in competition with electron extraction and limits the photocurrent. Despite the high density of trapped electrons, an intrinsically long lifetime for photogenerated holes in SrTiO3 photoanodes is observed using transient absorption spectroscopy, even in the absence of applied bias. This is important for overcoming the slow kinetics and hole accumulation associated with the water oxidation reaction, and for enabling good performance in photocatalytic systems where bias cannot be applied.
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Journal articleQuan Y, YiO MHN, Li Y, et al., 2023,
Influence of Bi co-catalyst particle size on the photocatalytic activity of BiOI microflowers in Bi/BiOI junctions - a mechanistic study of charge carrier behaviour
, Journal of Photochemistry and Photobiology A: Chemistry, Vol: 443, ISSN: 1010-6030Herein, we investigate the effect of Bi particle size in BiOI/Bi junctions on their photocatalytic function towards NO gas. BiOI microflowers (BiOI) and BiOI microflowers decorated with micron-sized Bi particles (BiOI/Bi MPs) were produced by a solvothermal method. BiOI decorated with nano-sized Bi particles (BiOI/Bi NPs) were produced by a reduction process. All samples were physically characterised by XRD, FT-IR, SEM, HR-TEM coupled with EDX analysis, DR-UV–visible and PL spectroscopy and functionally characterised by photocatalytic testing towards NO gas, TAS and EPR spectroscopy.Their photocatalytic activity towards NO gas was measured following ISO protocol (ISO 22197–1:2016). The best performing BiOI-based sample was BiOI/Bi NPs, showing NO and NOx conversion efficiencies of ∼33 and ∼11% under UVA light, and ∼26 and ∼8.1% under visible light, respectively. The BiOI and BiOI/Bi MPs samples showed significantly lower activities, displaying overall NOx conversion efficiencies of ∼3.5 and ∼0.8% under UVA light, respectively. Importantly, the best performing BiOI/Bi NPs samples showed visible light activity that was at least 6 times higher than that of a commercial TiO2 benchmark (CristalACTiVTM PC-S7). TAS measurements showed that charge carriers were significantly longer lived in the BiOI/Bi NPs sample (t50% from 10 μs of ∼90 μs) than the BiOI and BiOI/Bi MPs samples (t50% from 10 μs of ∼50 μs). This was attributed to the significant degree of interfacial contact formed between Bi and BiOI in the BiOI/Bi NPs sample, which enhanced charge carrier separation. EPR studies showed that this interfacial contact between BiOI and Bi likely promoted the formation of VO, which may have contributed to enhancement seen in photocatalytic activity in the BiOI/Bi junction.
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Journal articleMeng Z, Pastor E, Selim S, et al., 2023,
Operando IR optical control of localized charge carriers in BiVO4 photoanodes
, Journal of the American Chemical Society, Vol: 145, Pages: 17700-17709, ISSN: 0002-7863In photoelectrochemical cells (PECs) the photon-to-current conversion efficiency is often governed by carrier transport. Most metal oxides used in PECs exhibit thermally activated transport due to charge localization via the formation of polarons or the interaction with defects. This impacts catalysis by restricting the charge accumulation and extraction. To overcome this transport bottleneck nanostructuring, selective doping and photothermal treatments have been employed. Here we demonstrate an alternative approach capable of directly activating localized carriers in bismuth vanadate (BiVO4). We show that IR photons can optically excite localized charges, modulate their kinetics, and enhance the PEC current. Moreover, we track carriers bound to oxygen vacancies and expose their ∼10 ns charge localization, followed by ∼60 μs transport-assisted trapping. Critically, we demonstrate that localization is strongly dependent on the electric field within the device. While optical modulation has still a limited impact on overall PEC performance, we argue it offers a path to control devices on demand and uncover defect-related photophysics.
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Journal articleWang M, Kafizas A, Sathasivam S, et al., 2023,
ZnO/BiOI heterojunction photoanodes with enhanced photoelectrochemical water oxidation activity
, Applied Catalysis B: Environmental, Vol: 331, ISSN: 0926-3373ZnO/BiOI heterojunction photoanode thin films were prepared by aerosol-assisted chemical vapour deposition, and the impact of growth temperature and film thickness on the water oxidation functionality was systematically investigated. A top ZnO layer with a thickness of 120 nm (deposited at 350 °C) and a 390 nm thick BiOI layer (deposited at 300 °C) were found to achieve the best photoelectrochemical performance of the heterojunction. The ZnO/BiOI heterojunction exhibited a significant increase in photoelectrochemical activity, with a photocurrent of 0.27 mA·cm−2 observed at 1.1 VRHE (350 nm, 2.58 mW·cm−2), which is ~ 2.2 times higher than that of single-layer ZnO and far higher than that of BiOI. Photoluminescence spectroscopy and transient absorption spectroscopy measurements showed that there was effective charge transfer across the heterojunction which spatially separated charge carriers and increased their lifetime and ability to drive photoelectrochemical water oxidation.
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Conference paperCreasey G, McCallum T, O'Neill L, et al., 2023,
Materials and reactor development for photoelectrochemical hydrogen production
, Materials for Sustainable Development Conference (MATSUS), Publisher: Fundació de la comunitat valenciana SCITO
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Dr. Andreas Kafizas
Leader - Solar Coatings Group
e-mail: a.kafizas@imperial.ac.uk
tel: +44(0)20 7594 6752
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