Relative Band Positions Research Articles

Design of FeWO4@N-TiO2 nanocomposite and its enhanced photocatalytic activity in decomposing methylene blue and phenol under visible light

Effluents from textile industries contain high levels of methylene blue (MB) and phenol from other industries, which are serious health hazard and a threat to biodiversity as well as the environment. Nitrogen (N) doped TiO2 modified by iron tungstate (FeWO4) composite photocatalyst (FeWO4 @N-TiO2) working under visible light (λ ≥ 420 nm) could be a suitable candidate to degrade this pollutant. X-ray diffractometry (XRD) and X-ray Photoelectron Spectroscopy (XPS) study suggested that the N was introduced as substitutional doping into TiO2 lattice which leads to narrowing band gap of TiO2 nanoparticles. The prepared FeWO4 @N-TiO2 was utilized to measure efficiency in decomposing the methylene blue (MB) and phenol in aqueous phase under visible light (λ ≥ 420 nm) irradiation. The FeWO4 @N-TiO2 showed better catalytic efficiency to degrade MB and phenol in several compositions of FeWO4. The composite demonstrated 77% and 85% removal of MB and phenol from aqueous medium after 2 h of visible light illumination, respectively. Interestingly, radical-hole hunting identifying tests indicated the presence of hydroxyl radical (°OH) in the photocatalytic decomposition reaction medium. The higher efficiency of FeWO4 @N-TiO2 was originated from absorption of visible energy as well as the relative energy band positions of the components FeWO4 and N-TiO2. Thus, photoexcited electron (e‾) and hole (h+) could take part by inter-particle transfer through the formation of °OH radical which was experimentally confirmed and a photocatalytic reaction mechanism has been proposed to mineralize organics.

Fabrication of visible-light induced fluorine doped bismuth oxide (Bi2O3-xFx) photocatalyst in degrading textile dyes from wastewater

Discharge of unused and untreated dye effluents into the environment by the textile industries is a major issue. In this wastewater, the methylene blue (MB) and methyl orange (MO) remain in a dissolved state along with various pollutants at different levels. To remove these dyes, visible light (λ ​≥ ​420 ​nm) active F (fluorine) doped bismuth oxide (Bi2O3-xFx) photocatalyst was synthesized through facile sol-gel method utilizing bismuth oxide (Bi2O3) and hydrofluoric acid (HF). Bi2O3-xFx demonstrated enhanced photocatalytic activity to decompose methylene blue (MB) and methyl orange (MO) under visible light. The F content in Bi2O3-xFx composite was optimized to 0.94 atom % with respect to organics decomposition. The study showed that enhanced photocatalytic activity of Bi2O3-xFx was ascribed due to participation of photo-induced electron (e¯)-hole (h+) in photocatalysis. The existence of hole (h+) and the generated °OH radical was experimentally confirmed in aqueous medium. The formation mechanism of these reactive species was explained on the basis of relative energy band position of Bi2O3-xFx and a detail photocatalytic decomposition reaction mechanism was proposed.

Synthesis of CuO, ZnO and SnO2 Coupled TiO2 Photocatalyst Particles for Enhanced Photodegradation of Rhodamine B Dye

Environmental pollution is a global problem and dye pollution is one of the major factors. TiO2 shows promising photocatalytic properties that can degrade organic pollutants such as dye under ultraviolet (UV) irradiation. However, TiO2 possesses some disadvantages such as a wide band gap and a high recombination rate of electron-hole pairs. Coupling TiO2 with various metal oxides can enhance photocatalytic properties. In this work, photodepositon (reduction of metal ions on TiO2) followed by the thermal oxidation method were used for the coupling of TiO2 with CuO, ZnO, or SnO2 under various methanol concentrations (25 vol% or 50 vol%) and deposition duration (1 h or 3 h) to observe the effect of these parameters on the photocatalytic degradation activity on Rhodamine B (RhB) dye (up to 90 min). The rate constant of the photodegradation reaction (k) has improved from 0.0141 min−1 (uncoupled TiO2) to 0.0151~0.0368 min−1. Overall, CuO/TiO2 and SnO2/TiO2 samples have shown similar photocatalytic properties (average rate constants of 0.0341 min−1 and 0.0327 min-1, respectively), and both performed better than ZnO/TiO2 in terms of RhB photodegradation (average rate constants of 0.0197 min−1). The difference in photocatalytic performance can be explained by the bandgap of metal oxides and their relative band positions with TiO2. Lastly, CuO/TiO2 (50 vol%, 3 h) and SnO2/TiO2 (50 vol%, 3 h) have shown the best photocatalytic properties respectively due to a longer deposition time and higher concentration methanol, resulting in more deposited materials. Copyright © 2023 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

The hunt for formamide in interstellar ices

Context. Although solid-state pathways are expected to dominate the formation mechanisms of many complex organic molecules (COMs), very few COMs have been securely identified in interstellar ices, in stark contrast with the many COM detections in the gas phase. The launch of the James Webb Space Telescope (JWST) and its increase in sensitivity and spectral resolution opens the possibility of identifying more COMs in ices, but additional laboratory data are necessary. Formamide (NH2CHO) is one such COM that is of great interstellar and prebiotic relevance where more laboratory data are needed in the hunt for its presence in interstellar ices. Aims. This work aims to characterize the mid-IR spectra of formamide in its pure form as well as in mixtures of the most abundant interstellar ices via laboratory simulation of such ices, as well as to demonstrate how these laboratory spectra can be used to search for formamide in ice observations. Methods. Mid-IR spectra (4000–500 cm−1/2.5–20 μm) of formamide, both in its pure form as well as in binary and tertiary mixtures with H2O, CO2, CO, NH3, CH3OH, H2O:CO2, H2O:NH3, CO:NH3, and CO:CH3OH, were collected at temperatures ranging from 15–212 K. Results. Apparent band strengths and positions of eight IR bands of pure amorphous and crystalline formamide at various temperatures are provided. Three of these bands are identified as potential formamide tracers in observational ice spectra: the overlapping C = O stretch and NH2 scissor bands at 1700.3 and 1630.4 cm−1 (5.881 and 6.133 μm), the CH bend at 1388.1 cm−1 (7.204 μm), and the CN stretch at 1328.1 cm−1 (7.529 μm). The relative apparent band strengths, positions, and full width half maxima (FWHM) of these features in mixtures at various temperatures were also determined. All of the laboratory spectra are available to the community on the Leiden Ice Database for Astrochemistry (LIDA) for use in the interpretation of both observations (e.g., from JWST) and laboratory spectroscopic data. Finally, the laboratory spectra are compared to observational spectra of a variety of low- and high-mass young stellar objects as well as prestellar cores observed with the Infrared Space Observatory, the Spitzer Space Telescope, and JWST. A comparison between the formamide CH bend in laboratory data and the 7.24 μm band in the observations tentatively indicates that, if formamide ice is contributing significantly to the observed absorption, it is more likely in a polar matrix. Upper limits ranging from 0.35-5.1% with respect to H2O were calculated via scaling the formamide:H2O laboratory spectrum to the observations. These upper limits are in agreement with gas-phase formamide abundances and take into account the effect of a H2O matrix on formamide’s band strengths.

Advances in thin layer chromatography coupled with mass spectrometry technology

Thin layer chromatography (TLC) is a very useful liquid chromatography approach. The simple device, convenient operation, versatility, high throughput capabilities, low cost, and simple sample pretreatments make it widely employed in various fields. In recent years, TLC-MS has become one of the most prominent trends for this technology as developments of modern analytical technology and comprehensive application of different approaches. With the development and upgrading of medicine, food, and scientific instrument industries, it is believed that TLC-MS technology should play a better role and obtain an opportunity for development. This study reviewed TLC-MS interface technologies (most of which are in recent 10 years) based on more than 150 studies and classified these TLC-MS technologies as three strategies. The first is indirect coupling using commercially available interface instruments. The second is TLC-in-site detection directly with special MS ion source devices like fast-atom-bombardment desorption ionization, matrix-assisted laser desorption ionization, surface-assisted laser desorption ionization, electrospray-assisted laser desorption ionization, laser-induced acoustic desorption/electrospray ionization, electrostatic-spray ionization, easy ambient sonic-spray ionization, desorption sonic spray ionization, ionization using "desorption/ionization resource", ionization using "molecular ionization-desorption analysis source", multiwavelength laser desorption ionization, ionization using flowing afterglow-atmospheric pressure glow discharge, ionization low-temperature plasma probe, desorption/ionization induced using neutral clusters, ionization using inductively coupled plasma and so on. These MS analyses are performed after TLC development, thus, the relative position of the chromatographic bands on TLCs is invariable, and this analysis can be regarded as static detection, though flexible travel stages or conveyor belts can be introduced to move TLC plates. The third strategy is to monitor TLC run using MS in real-time just as the monitor employed in HPLC, in which the chromatographic bands are still moving. This strategy is generally run on forced-flow TLC techniques and is less examined. The typical coupling technologies (especially appeared in recent ten years) are summarized and briefly described in this study. TLC-MS has greatly enhanced the research efficiency of bioactive substances for food and drugs due to the widespread usage of TLC-bioautography technology. Nowadays, the main bottleneck in the development of TLC-MS is the design and commercialization of "plug and play" components. The high-throughput and real-time monitoring TLC-MS technology with flexible scanning functions is also expected. Furthermore, the comparative studies of different kinds of desorbing-ionizing technologies are also application problems for further discussion.

Design and synthesis of black phosphorus quantum dot sensitized inverse opal TiO2 photonic crystal with outstanding photocatalytic activities

Quantum dot sensitized photocatalyst is designed and applied in purification of dye wastewater, using black phosphorus nanoparticles (BPQDs) as the quantum dot and inverse opal (IO) TiO2 photonic crystal as the main photocatalyst. Due to electron density change within the composite, electrons can transfer from BPQDs to IO TiO2 directionally. Bandgap energies and relative energy band positions of BPQDs and IO TiO2 further provide efficient electronic transmission channels at the heterojunction interface. Therefore, interfacial resistance for charge transfer is reduced, the production of active oxidative species is promoted, and the photo induced charge transfer proceeds through a typical type-II route. Finally, excellent photocatalytic properties of BPQDs-IO TiO2 are achieved with the highest apparent kinetic constant (kapp) of 0.046 min−1, which is more than 3 times for bare IO TiO2 (0.014 min−1) and nearly 2 times for commercial P25 TiO2 (0.027 min−1). Furthermore, long-term stability and non-toxicity make the quantum dot sensitized photocatalyst have great applications in purifying environmental water pollution.

Characterization of Casirivimab Plus Imdevimab, Sotrovimab, and Bamlanivimab Plus Etesevimab-Derived Interference in Serum Protein Electrophoresis and Immunofixation Electrophoresis.

BackgroundTherapeutic monoclonal antibodies can be a source of assay interference in clinical serum protein electrophoresis (SPEP) and immunofixation electrophoresis (IFE), producing monoclonal bands that can be misinterpreted as a monoclonal gammopathy related to a B-cell or plasma cell neoplasm. The extent to which new anti-COVID-19 monoclonal antibodies produce this interference is unknown.MethodsCasirivimab plus imdevimab, sotrovimab, and bamlanivimab plus etesevimab were spiked into patient serum samples to evaluate for SPEP/IFE interference, to characterize the position of therapy-derived bands relative to a reference band (either combined beta band or beta 1 band, depending on instrument platform), and to confirm heavy and light chain utilization of each medication. Serum samples from patients who had recently received casirivimab plus imdevimab or sotrovimab were also evaluated for comparison.ResultsWhen spiked into serum samples, all tested anti-COVID-19 monoclonal antibodies generated interference in SPEP/IFE. Importantly, the patterns of interference differed between spiked serum samples and serum from patients who had recently received casirivimab plus imdevimab or sotrovimab.ConclusionsImdevimab can be added to the growing list of therapeutic monoclonal antibodies that produce sustained interference in SPEP/IFE. Although casirivimab and sotrovimab also produce assay interference in vitro, these antibodies are not reliably detected in serum from recently infused patients. The value of relative band position in recognizing bands that may represent therapeutic monoclonal antibodies is also emphasized. Clinicians and laboratorians should consider therapeutic monoclonal antibody interference in diagnostic SPEP/IFE and review a patient’s medication list when new or transient monoclonal bands are identified.

TD‐DFT modeling of electronic spectra of biliverdins in different environments

AbstractNon covalent biliproteins are found in a growing number of living organisms and even in viruses, such as SARS‐CoV‐2. Unlike the well described covalent biliproteins, such as the phytochromes, they present a vast structural and functional diversity, and often with limited experimental information. A very important tool (and sometimes the only one available) to study these systems is the UV–Vis spectrum, which is modulated both by conformational changes of the biliverdin chromophore and specific interactions with the apoprotein. In this work we present a theoretical study of the microscopic determinants of the UV–Vis spectrum of these compounds through the use of hybrid QM(TD‐DFT)/MM techniques and molecular dynamics simulations. Comparing our results with existing experimental data, we prove that it is possible to predict spectroscopic properties, such as relative position and intensity ratio of main bands, with affordable methods, and to provide a microscopic explanation of them. This systematic information can be very useful for the study of described biliproteins or for those yet unknown.

Photocatalytic dye degradation using nickel ferrite spinel and its nanocomposite.

Coloured wastewater is a major issue of today for human health and ecology. Among all available processes such as physical, chemical, biological and electrochemical methods, photocatalysis can be a promising solution because of its ability to degrade colour-causing compounds completely by converting them into simpler molecules (H2O, CO2) depending on dye structure. In this work, NiFe2O4was synthesized by the co-precipitation method. Furthermore, the composites of NiFe2O4 with TiO2 were synthesized by varying amounts of TiO2. The spinel and composites were characterized by XRD, ZETA analysis and UV-DRS. Their photocatalytic activities were investigated using the photocatalyticdegradation ofreactive turquoise blue 21 (RB 21)dye as model pollutants under sunlight.The increased absorption of the visible light and the enhanced separation of the electron-hole pairs due to the relative energy band positions in NiFe2O4 and TiO2 are considered as the main advantages.Our results showed that NiFe2O4-based nanocomposites could be used as an effective and magnetic retrievable photocatalyst.

Hidden Isomer of Trifluoroacetylacetone Revealed by Matrix Isolation Infrared and Raman Spectroscopy.

Enol forms of trifluoroacetylacetone (TFacac) isolated in molecular and rare gas matrices were studied using infrared (IR) and Raman spectroscopy. Additionally, calculations using DFT B3LYP and M06-2X as well as MP2 methods were performed in order to investigate the possibility of coexistence of more than one stable enol form isomer of TFacac. Calculations predict that both stable enol isomers of TFacac, 1,1,1-trifluoro-4-hydroxy-3-penten-2-one (1) and 5,5,5-trifluoro-4-hydroxy-3-penten-2-one (2), could coexist, especially in matrices where the room temperature population is frozen, 1 being the most stable one. Raman and IR spectra of TFacac isolated in nitrogen (N2) and carbon monoxide (CO) matrices exhibit clear absorption bands, which cannot be attributed to this single isomer. Their relative band positions and intensity profiles match well with the theoretical calculations of 2. This allows us to confirm that in N2 and CO matrices both isomers exist in similar amounts. Careful examination of the spectra of TFacac in argon, xenon, neon, normal, and para-hydrogen (Ar, Xe, Ne, nH2, and pH2 respectively) matrices revealed that both isomers coexist in all the explored matrices, whereas 2 was not considered in the previous spectroscopic works. The amount of the second isomer (2) in the as-deposited samples depends on the host. The analysis of TFacac spectra in the different hosts and under various experimental conditions allows the vibrational characterization of both chelated isomers. The comparison with theoretical predictions is also investigated.

Synthesis of g‐C3N4/InVO4 Semiconductor for Improved Photocatalytic and Photoelectrochemical Applications

AbstractIn this paper, graphite‐like carbon nitride‐indium vanadate (g‐C3N4/InVO4) composites have been synthesized via a mixing‐calcination method. Physico‐chemical and photocatalytic experiments suggested that the optimized g‐C3N4/InVO4 composite demonstrates highest photo‐activity in degrading Rhodamine B and para‐nitrophenol as target pollutants. The electrochemical impedance spectroscopic (Mott‐Schottky) analysis confirms n‐type semiconductivity for these materials whereas the composite material exhibited highest 13 μA/cm2 photocurrent under periodic UV‐Visible irradiation for water oxidation. The relative band positions indicate inter‐band interactions between heterojunctions of g‐C3N4 and InVO4 facilitating the separation and migration of photogenerated electron‐hole pairs and a stable performance was reported.

Do Particles Interact Electronically? —Proof of Interparticle Charge-transfer Excitation between Adjoined Anatase and Rutile Particles

Abstract Here, we report experimental evidence of interparticle spatial overlapping of orbitals to result in interparticle charge-transfer excitation (ICTE) at an anatase-rutile interface which is expected to be applicable to clarify the relative band position of metal-oxides and mixture homogeneity of mixture samples measured by reversed double-beam photoacoustic spectroscopy.

Photo sensitizing and electrochemical performance analysis of mixed natural dye and nanostructured ZnO based DSSC

The paper highlights the enactment of the natural dyes, like purple cabbage, spinach, turmeric and their mixture as a photo-sensitizer, with nanostructured zinc oxide (ZnO) as a photo-anode, based dye-sensitized solar cell (DSSC). The field emission scanning electron microscopic image of ZnO, prepared by chemical bath deposition process, proclaims two different types of morphology, nano-wire and nano-plate shape. The photo sensitizing properties of the natural dyes and their mixed part are explored through FTIR spectra and UV-vis light absorbance characteristics. The FTIR spectra explore the presence of different anchoring chemical groups which confirm the strong anchoring bond with ZnO and enhancement of electron mobility. The diffused reflectance spectra (DRS) of dye-loaded ZnO films incisive the absorption of dye on the mesoporous ZnO surface. The relative energy band positions of individual and mixed dye, yield stable execution of the cell that has been performed through the cyclic voltammeter. The driving force energy requirement for effortless transport of electron from the mixed dye to the conduction band of ZnO is revealed lowers (0.34 eV) as compared to individual dyes. Electrochemical impedance spectroscopy (EIS) analysis has been executed to find the charge transfer resistance, total bulk resistance, recombination loss through Nyquist plots and Bode plots. These characteristics pretense as the mixed dye has an eminent rate of electron transportation and lower recombination loss with longer electron lifetime. The photon to electrical power conversion efficiencies of purple cabbage, spinach, turmeric and their mix dyes are explored as 0.1015%, 0.1312%, 0.3045%, and 0.602%, respectively under same simulated light condition. The mixed dye reveals the stable performance of the cell with the highest conversion efficiency due to the absorption of an extensive range of the solar spectrum and well-suited electrochemical responses.

Insights for vibronic effects on spectral shapes of electronic circular dichroism and circularly polarized luminescence of aza[7]helicene.

We present a systematic study of vibrationally resolved absorption (ABS), electronic circular dichroism (ECD), emission (EMI), and circularly polarized luminescence (CPL) of aza[7]helicene. Because of the rare experience of theoretical CPL calculation, a variety of harmonic models have been employed to compute the vibronic structures. To fully understand the vibronic effects on the spectral shapes, Franck-Condon (FC) and Herzberg-Teller (HT) contributions, Duschinsky mixings and temperature effect have all been taken into consideration. The performance of different alternative approximate methods has been carefully compared and discussed in detail. The results show that Vertical Hessian (VH) model has a slight better performance on the spectral shapes than Adiabatic Hessian (AH), especially for CPL spectrum. The thermal excitation effect has led to a reduced resolution and a broader spectral width. The moderate HT effects on the different spectral shapes have been addressed. The dissymmetry factors have been correctly reproduced and the main vibronic features of the four different spectral shapes have been successfully captured. A good estimation of the overall spectral width, relative position and relative height of different spectral bands has been presented. The nice agreement with the experiment allows us to present a detailed interpretation of the spectral shapes.

Novel Ag2O-Ga2O3 type II p-n heterojunction as an efficient water cleanser for green cleaning technology

Ag2O-Ga2O3 based type II p-n nanoheterojunctions were fabricated using ex-situ chemical reduction technique with different densities of Ag2O attachment to gallia surface. A systematic optimization was carried out to establish the best performing junction aiming for the photodegradation of the noxious organic dye methyl orange (MO). Thorough theoretical and experimental studies were performed to determine relative band positions and ensure charge transfer between the counterparts. Favorable alignment of the electronic bands of Ag2O and Ga2O3 was identified as a key factor for the prompt separation of photogenerated e−/h+ pair leading to a faster decomposition of hazardous dyes. The optimized sample also performed remarkably fast in degrading carcinogenic phenol and other dyes like rhodamine B (RhB), aniline blue (AB), eosin B (EB) and mixtures of dyes with different ionic identities. Additional advantages of these catalysts were reflected in the retainment of catalytic efficiency over multiple water disinfection cycles and its performance in active media of different pH values was observed. With high degradation rate constants of 0.4158, 0.3306, 0.2436 and 0.207 min−1 for RhB, AB, MO, EB respectively and multidimensional performance as green cleaning agent, this newly explored Ag2O3-gallia nanoheterojunction is identified as a strong candidate for future water cleaning technology.

Study of structural and electronic properties of (ZnSeZB)m/(ZnSeWZ)n superlattices based on HSE hybrid functional

Using first-principles method, we studied systematically the structural and electronic properties of ZB/WZ superlattices of ZnSe. The band offsets are calculated by Heyd–Scuseria–Ernzerhof (HSE) hybrid functional which can give a good prediction on the relative band positions. The band alignment at ZB/WZ interface is found to be type-II with holes localized in wurtzite region and electrons in zinc-blende region, which is suitable for optoelectronic and solar energy conversion. The origin of type-II character and the carrier localization are investigated in detail.

(Invited) Interfacial Charge-Transfer Excitation at an Anatase-Rutile Junction: A Hypothesis

Titania, the most widely used metal oxide for photocatalytic applications, is categorized into semiconductor based on its electronic energy structure, and therefore its band structure, which must impact on the physicochemical properties of titania, is very important. We have developed a novel method for identification and characterization of metal-oxide powders with energy-resolved distribution of electron traps (ERDT) measured by reversed double-beam photoacoustic spectroscopy (RDB-PAS) [1,2]. In this study, ERDT patterns of anatase and rutile titania powders as well as their mixtures were measured and analyzed to elucidate the actual position of valence-band of two kinds of crystallites. Figure 1 shows ERDT patterns of ST-21 (anatase), ST-G1 (rutile) and their thoroughly brayed 50/50 mixture as well as simulated patterns by summing up to ST-21 and ST-G1 patterns with and without lower-side energy shift (ΔE = 0.19 eV) of the former. The degree of coincidence in the ERDT-pattern shape of observed and simulated mixtures, ζ, was calculated by changing ΔE to obtain the maximum ζ, 0.70, at ΔE =0.19 eV. If valence-band (VB) electrons are excited to ETs during RDB-PAS process independently in two titania samples, the mixture may give an ERDT pattern as simple summation. The results suggest that interfacial electron excitation from VB of ST-G1, which is slightly higher than that of ST-21, to ETs in ST-21. As has been already claimed that energy of ETs measured as energy from VBT in the ERDT patterns might be overestimated and electrons in a high-DOS part of VB (h-DOS(VB)), not VBT of the least DOS, are excited to ETs [1,2]. The above mentioned consideration may suggest that h-DOS(VB) of rutile is ca. 0.19 eV higher than that of anatase. Thus, RDB-PAS analysis of ERDT patterns of mixtures of different titania samples is a novel method to clarify the relative band position of semiconducting metal oxides such as titania. [1] A. Nitta, M. Takase, M. Takashima, N. Murakami, B. Ohtani, Chem. Commun., 52, 12096–12099 (2016). [2] A. Nitta, M. Takashima, N. Murakami, M. Takase, B. Ohtani, Electrochim. Acta, 264, 83–90 (2018). Figure 1

Carrier Dynamics Engineering for High-Performance Electron-Transport-Layer-free Perovskite Photovoltaics

Summary Electron-transport-layer-free (ETL-free) device architectures are promising designs for perovskite photovoltaics because they offer simpler configurations, low cost, and convenience for versatile optoelectronics. However, the development of ETL-free photovoltaics is hindered by their low performance. Herein, we reveal that a low electron-injection rate at the ETL-free interface is responsible for the performance loss. Moreover, we demonstrate that improving carrier lifetimes in the perovskite films can remedy the poor carrier extraction at interfaces, enabling carrier collection efficiency in ETL-free photovoltaics to approach that in ETL-containing devices. Using perovskite films with microsecond carrier lifetimes, we obtained ETL-free devices with a power conversion efficiency (PCE) of 19.5%, nearly eliminated hysteresis, and good stability. Such a PCE value is comparable to that (20.7%) of the analogous ETL-containing photovoltaics. These results offer opportunities for ETL-free architecture designs in the perovskite photovoltaics family. More importantly, this research provides a general approach to improving the performance of photovoltaics with low-injection-rate interfaces.

Synthesis of g-C3N4/Bi5O7I microspheres with enhanced photocatalytic activity under visible light

Novel g-C3N4/Bi5O7I heterojunction microspheres having excellent photocatalytic activity were successfully prepared by a one-pot ethylene glycol (EG)-assisted hydrothermal method followed by calcination in air. Bi5O7I microspheres grafted with g-C3N4 nano-sheets were formed and studied by electron microscopy. The morphological effects on g-C3N4/Bi5O7I photocatalytic capability with varied g-C3N4 contents were investigated and discussed. The g-C3N4/Bi5O7I microspheres exhibited much improved photocatalytic degradation performance under visible light irradiation compared with bare Bi5O7I and g-C3N4. The preparation conditions of g-C3N4/Bi5O7I microspheres with optimal photocatalytic ability for degrading methyl orange (MO) and rhodamine (RhB) were established. Analyses by both photoluminescence (PL) and photocurrent independently confirmed that photo-induced electron-hole pairs in the g-C3N4/Bi5O7I composite have been effectively created which was responsible for the observed photocatalysis. Based on the analysis of the experiment results, a Z-Scheme heterojunction photocatalytic mechanism was proposed. The excellent photocatalytic performance could be attributed to the effective charge separation at the interface between g-C3N4 and Bi5O7I and the enhanced visible light absorption. In addition, the photocatalytic mechanism was discussed on the basis of the relative band positions of these two semiconductor materials.

Structural, vibrational, and electronic properties of single-layer hexagonal crystals of group IV and V elements

Using first-principles density functional theory calculations, we investigate a family of stable two-dimensional crystals with chemical formula $A_2B_2$, where $A$ and $B$ belong to groups IV and V, respectively ($A$ = C, Si, Ge, Sn, Pb; $B$ = N, P, As, Sb, Bi). Two structural symmetries of hexagonal lattices $P\bar{6}m2$ and $P\bar{3}m1$ are shown to be dynamically stable, named as $\alpha$- and $\beta$-phases correspondingly. Both phases have similar cohesive energies, and the $\alpha$-phase is found to be energetically favorable for structures except CP, CAs, CSb and CBi, for which the $\beta$-phase is favored. The effects of spin-orbit coupling and Hartree-Fock corrections to exchange-correlation are included to elucidate the electronic structures. All structures are semiconductors except CBi and PbN, which have metallic character. SiBi, GeBi and SnBi have direct band gaps, whereas the remaining semiconductor structures have indirect band gaps. All structures have quartic dispersion in their valence bands, some of which make the valence band maximum and resemble a Mexican hat shape. SnAs and PbAs have purely quartic valence band edges, i.e. $E{\sim}{-}\alpha k^4$, a property reported for the first time. The predicted materials are candidates for a variety of applications. Owing to their wide band gaps, CP, SiN, SiP, SiAs, GeN, GeP can find their applications in optoelectronics. The relative band positions qualify a number of the structures as suitable for water splitting, where CN and SiAs are favorable at all pH values. Structures with quartic band edges are expected to be efficient for thermoelectric applications.