Suitable Band Gap Energy Research Articles

Ultraviolet antireflective porous nanoscale periodic hole array of 4H-SiC by Photon-Enhanced Metal-assisted chemical etching

Benefitting from the outstanding stability and suitable bandgap energy, silicon carbide (SiC) shows promising applications especially for ultraviolet light detection in harsh environments. Traditionally, 4H-SiC surface antireflection textures which boost light harvesting have been realized by plasma dry etching due to its chemical inertness, nevertheless causing surface damage which is detrimental to device performance. This paper presents 4H-SiC porous nanoscale periodic hole array with outstanding ultraviolet antireflection capability by highly efficient plasma-free photon-enhanced metal-assisted chemical etching. Its formation process is carefully monitored with etching mechanism explained by carrier generation and mass transport. Effect of pattern dimension on etching is also investigated, which is closely related with catalyst coverage. The 4H-SiC porous nanoscale periodic hole array by photon-enhanced metal-assisted chemical etching sheds light on novel applications in ultraviolet light harvesting and detection.

Physical Properties of Candidate X-Ray Detector Material Rb4Ag2BiBr9.

Recently, metal halide perovskites have emerged as promising semiconductor candidates for sensitive X-ray photon detection due to their suitable bandgap energies, excellent charge transport properties, and low material cost afforded by their low-temperature solution-processing preparation. Here, we report an improved methodology for single crystal (SC) growth, thermal and electrical properties of a two-dimensional (2D) layered halide material Rb4Ag2BiBr9, which has been identified as a potential candidate for X-ray radiation detection applications. The measured heat capacity for Rb4Ag2BiBr9 implies that there are no structural phase transitions upon cooling. Temperature dependence of thermal transport measurements further suggest remarkably low thermal conductivities of Rb4Ag2BiBr9 that are comparable to the lowest reported in literature. The bulk crystal resistivity is determined to be 2.59×109 Ω·cm from the current-voltage (I-V) curve. Density of trap states are estimated to be ~1010 cm-3 using the space-charge-limited-current (SCLC) measurements. The fabricated Rb4Ag2BiBr9-based X-ray detector shows good operational stability with no apparent current drift, which may be ascribed to the 2D crystal structure of Rb4Ag2BiBr9. Finally, by varying the X-ray tube current to change the corresponding dose rate, the Rb4Ag2BiBr9 X-ray detector sensitivity is determined to be 222.03 uCGy-1cm-2 (at an electric field of E = 24 V/mm).

The Deposition of Titanium Dioxide Nanostructures Layer Using One-step Solution Process and Spin-coating Technique

Background: Titanium dioxide (TiO2) is an oxide-based material that has been recently discovered by many researchers owing to its properties such as a good absorber with excellent optical properties and the best stability compared to lead, Pb, which is not stable in the ambient air and is a toxic material. TiO2 is a non-toxic material and is not hazardous to the environment. TiO2 became a favored choice in selecting as a layer because of faster electron extraction and suitable bandgap energy. Objective: In this study, we deposited and optimized TiO2 at different TiO2 precursor molar concentrations varying between 0.005 - 0.05M. Methods: A one-step solution process and a low-temperature processing spin-coating technique were used. Results: Using the field emission scanning electron microscope, it was found that the surface morphology of the TiO2 Nanostructures Layer (NsL) was evenly distributed, presenting a homogeneous surface. An atomic force microscope showed that the TiO2 NsL appeared as a uniform, dense and compact surface close to each other. It was revealed that the surface roughness value (RMS) was 47.72nm, and the thickness of TiO2 NsL (Pmax) was 26.82nm. Besides, the surface coverage was good and uniform, while the percentage of surface roughness was found to be 11.8% using a surface profiler. The Ultra-violet visible spectroscopy showed the bandgap energy of 3.11 eV. Conclusion: The optimum result suggests that TiO2 NsL, as an electron transport layer (ETL), could be used for fabrication in the architecture engineering structure of Bi- perovskite based solar cell devices in the future.

Growth of Cu2ZnSnS4 thin film absorber layer on transparent conductive oxides and molybdenum substrates by electrodeposition for photovoltaic application

Cu2ZnSnS4 (CZTS) absorber layer for the photovoltaic application was successfully deposited on different substrates, indium tin oxide (ITO), fluorine-doped tin oxide (FTO) and molybdenum (Mo) using a single step electrodeposition process. The structural, morphological and optical properties of the CZTS films were analyzed by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), and photoluminescence (PL). The present study was designed to determine the effect of the substrate on the kesterite thin film properties grown by electrodeposition. The results confirm that the CZTS properties depend on the substrate nature. Furthermore, the CZTS films deposited on Mo substrate was found more appropriate for CZTS based solar cells due to their crystallinity and good morphology as well as their suitable energy bandgap around 1.6 eV.

Composition-dependent activity of ZnxCd1-xSe solid solution coupled with Ni2P nanosheets for visible-light-driven photocatalytic H2 generation

Metal selenide semiconductors have been rarely used for photocatalytic water splitting because of their poor stability and severe photocorrosion properties. Hence, designing stable metal selenides with suitable bandgap energies has considerable practical significance in photocatalytic H2 evolution. In this work, a novel series of ZnxCd1-xSe (x = 0 ∼ 1) with tunable band structure were fabricated through a simple solvothermal method. Impressively, the ZnSe exhibited a maximum H2 production rate of 1056 µmol g−1h−1, which was higher than that of CdSe and ZnxCd1-xSe solid solutions. Such visible-light photoactivity for water reduction to H2 was attained even after 6 cycling photocatalytic experiments. Moreover, the two-dimensional (2D) Ni2P nanosheets act as a high-efficiency cocatalyst integrated with ZnxCd1-xSe semiconductor to boost photocatalytic H2 generation performance. The optimal 8% Ni2P/ZnSe composites displayed excellent cycling stability and superior photocatalytic H2 evolution performance (4336 µmol g−1h−1), which was about 4.1 times that of pure ZnSe under visible light irradiation. Photoelectrochemical (PEC), photoluminescence (PL), and time-resolved photoluminescence (TRPL) measurements reveal that the improved photoactivity Ni2P/ZnSe photocatalysts were ascribed to the effective separation and migration of photoinduced carriers. The present work paves a pathway to explore the fabrication of ZnxCd1-xSe solid solutions and the hybridization of 2D transition metal phosphides nanosheets toward photocatalytic applications.

Freeze-dried dicyandiamide-derived g-C3N4 as an effective photocatalyst for H2 generation

BackgroundHydrogen (H2) is viewed as a clean, green, and sustainable energy source. The photocatalytic H2 evolution using light-activated photocatalyst under light irradiation is attractive to convert light into chemical energy in a feasible way. In the present work, photocatalysis of H2 generation was explored, using graphitic carbon nitride (g-C3N4) synthesized from freeze-dried dicyandiamide (DICY). MethodsThe DICY underwent rapid dissolution-recrystallization during the freeze-drying process, enabling more complete polymerization of the heptazine units of g-C3N4 than occurred in the same compound synthesized from untreated DICY. After loading with Pt as a cocatalyst, and under light irradiation (metal halide lamp) in the presence of triethanolamine, g-C3N4 synthesized from freeze-dried DICY (DCN) showed an increased H2 evolution rate (∼20 μmol h‒1) compared with that using g-C3N4 derived from untreated DICY (CN) (12 μmol h‒1). In addition, DCN had a higher H2 generation rate than CN under light of different wavelengths (400, 450, and 550 nm). Significant FindingsThe improved activity of DCN could be attributed to inhibition of charge recombination (evidenced by photoluminescence), fast charge transfer (evidenced by electrochemical impedance spectra and photocurrent measurements), and a suitable energy bandgap (evidenced by Mott-Schottky and UV–vis measurements) resulting from better-polymerized heptazine rings (evidenced by nuclear magnetic resonance spectroscopy). In summary, DCN prepared in this study could be used as a visible-light activated and effective metal-free material for photocatalytic H2 generation.

α-Fe2O3 nanostructure-based gas sensors

Gas sensors based on semiconducting metal oxides have attracted considerable attention for various applications owing to their facile, cheap, and small-scale manufacturing processes. Hematite (α-Fe2O3) is widely considered as a promising candidate for a gas-sensing material owing to not only its abundance in the earth’s crust and low price but also its chemical stability and suitable bandgap energy. However, only a few studies have been performed in this direction because of the low gas response and sluggish response of hematite-based gas sensors. Nanostructures present a representative solution to both overcome these disadvantages and exploit the desirable features to produce high-performance gas sensors. However, several challenges remain for adopting gas sensors based on metal oxide nanostructures, such as improving cost efficiency and facilitating mass production. This review summarizes the recent studies on gas sensors based on hematite nanostructures. It also provides useful insights into various strategies for enhancing the gas-sensing properties of gas sensors based on hematite nanostructures.

Bi2WO6 nanoflakes incorporated carbon nanofibers to control biological and chemical pollutants: bifunctional application

CNFs-Bi2WO6 nanocomposite was synthesized by hydrothermal method. The physico-chemical characterization of samples was done by XRD, SEM-EDX, UV-DRS, and PL spectra. CNFs-Bi2WO6 nanocomposite has shown better photodegradation efficiency than pristine Bi2WO6 for Rhodamine B dye under visible light irradiation. The addition of Bi2WO6 to pure carbon nanofibers (CNFs) facilitated absorption of light as well as assisted in separation of electron-hole pairs which ultimately lead to superior photodegradation efficiency. The CNFs-Bi2WO6 nanocomposite displayed excellent photocatalytic efficiency under visible light for dye degradation, owing to the synergistic effect of CNFs and Bi2WO6 with excellent charge separation characteristics and suitable band gap energy. The CNFs-Bi2WO6 nanocomposite was also screened for antimicrobial potential against two bacterial strains and one pathogenic fungal strain Candida albicans. The fabricated CNFs demonstrated antimicrobial activity, which was fortified due to inclusion of Bi2WO6 nanoflakes.

High-Lying 31Ag Dark-State-Mediated Singlet Fission.

Singlet fission (SF), the conversion of one high-energy singlet to two low-energy triplets, provides the potential to increase the efficiency of photovoltaic devices. In the SF chromophores with C2h symmetry, exemplified by polyenes, singlet-to-triplet conversion generally involves a low-lying 21Ag dark state, which serves as either a multiexciton (ME) intermediate to promote the SF process or a parasitic trap state to shunt excited-state populations via internal conversion. This controversial behavior calls for a deep understanding of dark-state-related photophysics involving the higher-lying singlet state. However, the optical "dark" and "transient" nature of these dark states and strong correlation feature of double exciton species make their characterization and interpretation challenging from both experimental and computational perspectives. In the present work combining transient spectroscopy and multireference electronic structure calculations (XDW-CASPT2), we addressed a new photophysical model, i.e., a high-lying 31Ag dark-state-mediated ultrafast SF process in the benzodipyrrolidone (BDPP) skeleton. Such a 31Ag dark state with distinctive double excitation character, described as the ME state, could be populated from the initial 11Bu bright state on an ultrafast time scale given the quasi-degeneracy and intersection of the two electronic states. Furthermore, the suitable optical band gap and triplet energy, high triplet yield, and excellent photostability render BDPP a promising SF candidate for photovoltaic devices. These results not only enrich the arsenal of SF materials but also shed new insights into the understanding of dark-state-related photophysics, which could promote the development of new SF-active materials.

Porous hollow Ag/Ag2S/Ag3PO4 nanocomposites as highly efficient heterojunction photocatalysts for the removal of antibiotics under simulated sunlight irradiation

Antibiotic pollutants are a serious and growing threat to human health and the environment that efficient measures must be taken to eliminate them. Here, we report the facile fabrication of porous hollow Ag/Ag2S/Ag3PO4 heterostrucutres for efficient photocatalytic degradation of tetracycline under simulated sunlight irradiation. The morphology manipulation and hetero-nanocomposites construction through a coprecipitation-refluxing approach were applied to enhance the photocatalytic performance of the Ag/Ag2S/Ag3PO4 products. The photodegradation outcomes indicated that the heterojunction Ag/Ag2S/Ag3PO4 photocatalyst with a suitable band gap energy of 2.17 eV, has better degradation performance (∼95%) than individual Ag2S and Ag3PO4 structures after 120 min of simulated sunlight irradiation, even after five recycles. The good photocatalytic activity of Ag/Ag2S/Ag3PO4 nanocomposites could be mainly attributed to the unique hierarchical architectures, promoted visible-light harvesting, reduced a recombination and boosted separation of electron-hole pairs originated from the as-formed heterojunctions. Moreover, we proposed a photocatalytic degradation mechanism based on the radical scavenging results, which disclosed that the •O2− and •OH species perform essential tasks for the photodegradation of antibiotics by Ag/Ag2S/Ag3PO4 nanocomposites.

Efficient photocatalytic desulfurization of thiophene under visible light irradiation over flower-like AgBiS2 photocatalyst

Here, we report the production of hierarchical flower-like AgBiS2 nanostructuresby an amino acid-modified polyol route. This work indicates that by changing thepolyol process conditions including kind of capping agent, reaction time and refluxtemperature, the sheet-like, cone-like, sphere-like and flower-like morphologies ofAgBiS2 micro/nanostructures can be prepared. The phase, elemental composition,morphology and optical characteristics of as-prepared AgBiS2 nanostructures wereanalyzed by UV–Vis, FESEM, XRD, and EDS techniques. After characterization ofthe products, the AgBiS2 nanostructures were employed as novel photocatalystsfor oxidative desulfurization of thiophene/n-octane solution as model fuel undervisible light illumination. Results demonstrate that hierarchical flower-like AgBiS2photocatalyst with desirable band gap energy (2.44 eV) has high photocatalyticdesulfurization performance of about 89% after 2 h of visible light irradiation.As well as, the effects of morphology, photocatalyst dosage and reusability ofthe AgBiS2 nanostructures on the photocatalytic performance were evaluated.The excellent photocatalytic activity of AgBiS2 photocatalyst can be attributedto the strong visible light absorption, high separation rate of electron–hole pairs,special hierarchical structures and suitable band gap energy. Moreover, a reliablephoto-oxidation desulfurization mechanism was discussed according to theactive species trapping experiments, which revealed the photo-generated h+ and•O2 − radicals were the main active species in the photocatalytic desulfurizationprocess.

Crystal growth, electronic and optical properties of Tl2CdSnSe4, a recently discovered prospective semiconductor for application in thin film solar cells and optoelectronics

Abstract A single crystal of the non-centrosymmetric low-temperature modification of Tl2CdSnSe4 (space group I 4 ‾ 2m) was grown, for the first time, and its electronic and optical properties were studied from both experimental and theoretical viewpoints. The Tl2CdSnSe4 crystal was grown from the solution-melt by vertical Bridgman-Stockbarger method. Centimeter dimensions of the crystal allow its application in practice. The bandgap energy, Eg = 1.32 eV, estimated from the optical absorption coefficient agrees well with the value of Eg = 1.29 eV calculated from the photosensitivity measurements. X-ray photoelectron spectroscopy (XPS) was used to investigate the electronic structure and charge states of atoms composing the crystal under consideration. To detect the best agreement of the curve of total densities of states (DOS) with the experimental XPS spectrum of valence electrons of Tl2CdSnSe4, we performed theoretical calculations within a density functional theory (DFT) framework treating different models for exchange correlation (XC) potential. Our findings yield that the best agreement of the experimental and theoretical distributions of the valence electronic states is derived when using in the computation procedure for XC potential the modified Becke-Johnson potential in the form of Tran-Blaha (TB-mBJ), which involves also the Hubbard parameter U for strongly correlated d electrons and spin-orbit coupling (SOC) effect (TB-mBJ + U + SOC model). Based on this approach, we calculated partial densities of states, energy band dispersion, and main optical constants of Tl2CdSnSe4. Importantly, the TB-mBJ + U + SOC model reveals the Eg value which is close to those determined experimentally; therefore, scissors correction adjustment is not required when performing DFT calculations of the optical constants in such a case. The present experimental XPS measurements of the treated with middle-energy Ar+-ions Tl2CdSnSe4 crystal surface and the theoretical DFT calculations data indicate, in spite of its rather hazardous chemical elements, thallium and cadmium, the crystal surface is rather stable and, coupled with suitable energy band gap, makes quaternary selenide under discussion a very promising material for using in thin film solar cells and optoelectronics as well as in highly efficient photocatalytic devices.

Facile precipitation synthesis of extraordinary visible‐light‐driven BiOXs photocatalyst

Bismuth halide oxide with three halogen elements (P-BiOXs) catalyst was prepared by a facile precipitation method at room temperature only for 30 min. Several measurement technologies were employed to characterise the structures and morphologies of the obtained samples. Coloured Rhodamine B (RhB), methyl orange (MO), methylene blue (MB) and colourless bisphenol A (BPA) were selected to evaluate the photocatalytic activity of the samples. The experimental results showed the P-BiOXs thin nanoplates exhibited the most excellent photocatalytic activity among the prepared samples for the degradation of MO under visible light illumination. More importantly, the catalyst P-BiOXs could effectively degradate RhB, MB and BPA. The P-BiOXs catalyst displayed good photocatalytic stability by the recycling tests. The highly efficient visible light catalytic properties of P-BiOXs could be due to the high specific surface area, enhanced light-harvesting ability, the suitable bandgap energy and the lower recombination rate of the photogenerated electrons and holes.

Altered Properties of TiO2 for Photocatalytic Oxidative Desulphurisation

Photocatalytic oxidative desulphurisation has become a promising technique as a result of its high capability, mild reaction conditions, economical, and low energy usage. In the present study, copper oxide doped on titanium dioxide (CuO/TiO2) was prepared by facile electrolysis method. The presence of mesoporous materials with high surface area was confirmed by nitrogen (N2) adsorption-desorption analysis where the band gap energies were determined by ultraviolet-visible diffuse reflectance spectra (UV-Vis DRS). The photoactivity testing on desulphurisation of 100 mg L-1 dibenzothiophene (DBT) revealed the highest extraction (7.5 x 10-3 mM min-1) and photooxidation rates (1.8 x 10-3 mM min-1), which were acquired by 0.8 g L-1 Cu0.1T0.9 after 2 h under visible irradiation. This is attributed by the well dispersion of CuO on TiO2, suitable band gap energy, and better charge carrier separation by the synergistic interaction of both materials.

Optimized Synthesis Temperature and Time to Obtain Crystalline Carbon Nitride with Enhanced Photocatalytic Activity for Phenol Degradation

In this work, the crystalline carbon nitride photocatalysts were synthesized by an ionothermal technique with varied synthesis temperature of 500, 550, and 600 °C, and synthesis time of 2, 4, and 6 h. Fourier transform infrared spectra showed the successful formation of the prepared carbon nitrides from their characteristic vibration peaks. X-ray diffraction patterns suggested that the same phase of poly(triazine imide) and heptazine could be observed, but with different crystallinity. The optical properties showed that different temperatures and synthesis time resulted in the different band gap energy (2.72–3.02 eV) as well as the specific surface area (24–73 m2 g–1). The transmission electron microscopy image revealed that the crystalline carbon nitride has a near-hexagonal prismatic crystallite size of about 50 nm. Analysis by high-performance liquid chromatography showed that the best photocatalytic activity for phenol degradation under solar light simulator was obtained on the crystalline carbon nitride prepared at the 550 °C for 4 h, which would be due to the high crystallinity, suitable low band gap energy (2.82 eV), and large specific surface area (73 m2 g–1). Controlling both the temperature and synthesis time is shown to be important to obtain the best physicochemical properties leading to high activity.

Synthesis and Photocatalytic Activity of Ni–Fe Layered Double Hydroxide Modified Sulphur Doped Graphitic Carbon Nitride (SGCN/Ni–Fe LDH) Photocatalyst for 2,4-Dinitrophenol Degradation

In this work, visible light-active sulphur doped graphitic carbon nitride coupled with Ni–Fe layered double hydroxide (SGCN/Ni–Fe LDH) was prepared through co-precipitation procedure using commercially available thiourea, nickel nitrate, and ferric nitrate. The surface morphology characterization showed LDH crystallite growth onto the surface of SGCN, exploiting the delocalized π-electrons of graphitic structure to attain chemical stability. The synthesized photocatalyst exhibited 98% 2,4-dinitrophenol (DNP) photodegradation within 120 min of visible light irradiations, which was surprisingly high compared to 60 and 55% obtained for bare GCN and Ni–Fe LDH samples. This photo removal efficiency could be due to suitable bandgap energy, layered graphitic and brucite Ni–Fe layered structures, and sufficient pollutant adherence to active sites provided by incorporation of S dopant into bare GCN. The characterization results obtained by cyclic voltammetry graph photoluminescence and electrochemical impedance spectra indicated minimum charge carrier recombination due to the type-II charge transfer route along with an active generation of ⋅O2− and h+ as dominant reactive species participating in DNP mineralization into more unaffected inorganic ions. The photocatalytic activity enhanced in an acidic medium at optimized parameters, i.e., pH 4, photocatalyst dosage 50 mg in 50 mL solution, and DNP concentration 1.0 × 10−4 mol/dm3, due to ionic interactions between negatively charged DNP and positive intercalated structure of Ni–Fe LDH. The as-prepared photocatalyst photodegradation ability was retained after 5 catalytic cycles, confirming its environmentally-compatible usage in water treatment.

The unforeseen relationship of Fe2O3 and ZnO on fibrous silica KCC-1 catalyst for fabricated Z-scheme extractive-photooxidative desulphurization

Fibrous silica KAUST Catalysis Centre (KCC-1) was prepared via a hydrothermal-microwave method, followed by incorporation of Fe2O3 and ZnO by an electrochemical technique to give ZnO-Fe2O3/KCC-1 (ZFK) catalysts. XRD, FESEM, N2 physisorption, FTIR, XPS, ESR and UV–Vis DRS were employed to characterize the catalysts. A varied amount of Fe2O3 and ZnO seems have insightful impact on the physicochemical behaviours of the KCC-1 while prominently enhanced the extractive-photooxidative desulphurization of dibenzothiophene (DBT). 5Z10FK demonstrated the best performance mainly due to a well distribution of both metal oxides on KCC-1, the highest Si-O-Fe and Si-O-Zn bonds, an appropriate amount of surface defect and suitable band gap energy. Besides, the suitable band positions of 10FK and 5ZK in 5Z10FK composite has allowed the formation of Z-scheme heterojunction for conserved strong redox potential. Kinetic studies revealed that the adsorption of DBT was the rate determining step, thus this reaction obeyed the Langmuir-Hinshelwood pseudo-first order.

Computational screening of vdWs heterostructures of BSe with MoSe2 and WSe2 as sustainable hydrogen production materials

Recently, fabricating type-II vertical van der Waals (vdWs) heterostructure is a promising material for hydrogen production. The absorption capability, charge density distributions, band alignments and electronic properties of the monolayers and heterostructures are systematically investigated using computational studies. Using ab initio molecular dynamics, binding energy and phonon calculations, the stability of the heterostructures are verified. Both heterostructures are type-II materials, which can increase the separation of charge carriers. Moreover, the charge density difference and the potential drop across the interface of MSe2/BSe creates a high built-in electric field that can prevent the recombination of charge carriers. We found that the visible-light optical properties of both heterostructures are much enhanced with suitable bandgap energy for water splitting. The band alignment suggests that the heterostructures straddle water redox potentials in acid solutions (0 < pH < 7). Our study predicted that MSe2/BSe vdW heterostructures have great potential for photocatalytic hydrogen production.

Enhanced sono-photocatalytic activity of AgCl0.75Br0.25 with different dimensional graphene

Degradation of pesticide residues by ultrasonic-assisted photocatalytic technology with a semiconductor catalyst is an effective method to reduce environmental wastewater pollutant. At present, researchers devote enormous time and energy to exploit new-type semiconductor catalysts which have larger specific surface area and suitable bandgap energy. While, there are few researches to explore the effect on the semiconductors composites with different dimensional material. Herein, we successfully immobilized spherical-like AgCl0.75Br0.25 particles on skeleton surface of reduced graphene oxide (RGO) with different dimensions (0D, 2D, 3D) via the photo-ultrasonic method for the first time. The results indicated that AgCl0.75Br0.25 demonstrated distinctly different specific surface areas, light harvesting ability and charge carrier separation efficiency after coupling with different dimensional RGO. Particularly, the 3D RGO/AgCl0.75Br0.25 composite revealed the optimal ultrasound-assisted photocatalytic activity for removal of chloridazon (Chl), and its degradation efficiency had reached at 75.2%, which was about 1.83, 1.27, and 1.19 times higher than that of pristine AgCl0.75Br0.25 (41%), 2D RGO/AgCl0.75Br0.25 (59.2%) and 0D RGO/AgCl0.75Br0.25 (63.4%), respectively. Moreover, the cyclic degradation experiments suggested that the 3D RGO/AgCl0.75Br0.25 composite had excellent sono-photocatalytic stability and repeatability. The radicals trapping experiments revealed that ·OH and h+ were the main reactive species in the ultrasound-assisted photocatalytic degradation process, and the possible mechanism was further proposed based on above results. Overall, this work could provide an effective strategy to construct the heterojunction semiconductors with excellent ultrasound-assisted photocatalytic activity to alleviate environmental wastewater pollution.

Br-doping of g-C3N4 towards enhanced photocatalytic performance in Cr(VI) reduction

Semiconductor photocatalytic technology is widely recognized as one of the most promising technologies to solve current energy and environmental crisis, due to its ability to make effective use of solar energy. In recent years, graphite carbon nitride (g-C3N4), a new type of non-metallic polymer semiconductor photocatalyst, has rapidly become the focus of intense research in the field of photocatalysis because of its suitable bandgap energy, unique structure, and excellent chemical stability. In order to improve its intrinsic shortages of small specific surface area, narrow visible light response range, high electron-hole pair recombination rate, and low photon quantum efficiency, a simple method was utilized to synthesize Br-doped g-C3N4 (CN–BrX, X = 5, 10, 20, 30), where X is a percentage mole ratio of NH4Br to melamine. Experimental results showed that Br atoms were doped into the g-C3N4 lattice by replacing the bonded N atoms in the form of C–N=C, while the derived material retained the original framework of g-C3N4. The interaction of Br element with the g-C3N4 skeleton not only broadened the visible-light response of g-C3N4 to 800 nm with an adjustable band gap, but also greatly promoted the separation efficiency of the photogenerated charge carrier and the surface area. The photocurrent intensity of bare CN and CN–BrX (X = 5, 10, 20, 30) catalysts is calculated to be 1.5, 2.0, 3.1, 6.5, and 1.9 μA, respectively. And their specific surface area is measured to be 9.086, 9.326, 15.137, 13.397, and 6.932 m2/g. As a result, this Br-doped g-C3N4 gives significantly enhanced photocatalytic reduction of Cr(VI), achieving a twice enhancement over g-C3N4, with high stability during prolonged photocatalytic operation compared to bare g-C3N4 under visible light irradiation. Furthermore, an underlying photocatalytic reduction mechanism was proposed based on control experiments using radical scavengers.