Valence Band Position Research Articles

S-doped copper selenide thin films synthesized by chemical bath deposition for photoelectrochemical water splitting

The utilization of fossil fuels to meet ever-increasing energy demands is causing a significant threat to the Earth's climate and its inhabitants. To address this issue, photoelectrochemical (PEC) water splitting has emerged as a promising solution to produce oxygen (O2) and hydrogen (H2) in a cost-effective, environmentally friendly, clean, and renewable manner. In this study, we present the development of cost-effective Cu3Se2 and S-doped Cu3Se2 thin films on Fluorine-doped Tin Oxide (FTO) substrates using a chemical bath deposition (CBD) process to enhance the efficiency of PEC water oxidation to produce oxygen. The X-Ray Diffraction (XRD) pattern confirms the presence of a single-phase tetragonal Cu3Se2 crystal structure with a noticeable shift in the characteristic (211) reflection towards a higher 2θ value, from 38.1° to 38.4°, indicating the successful doping of S in the Cu3Se2 thin films. To further validate successful S doping in the Cu3Se2 crystal lattice, X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray (EDX), Fourier transform infrared (FTIR), and Raman Spectroscopy were employed. TEM reveals a granular structure with an average particle size of 7–8 nm, which is consistent with the crystallite size determined by XRD. Furthermore, the valence band and conduction band edge positions are found to be 1.56 and −0.57 eV, respectively. The presence of S increased the band gap of Cu3Se2, from 1.97 to 2.15 eV, thus confirming the bending of the band edge upon doping. The specific surface areas (SSA) of pristine and S-doped Cu3Se2 were determined to be 5.03 and 111.48 m2g−1, respectively, showing a twenty-two-fold increase upon doping. The PEC performance of the materials was evaluated through chopped chronoamperometry (CA), linear sweep voltammetry (LSV), electrochemical impedance spectroscopy (EIS), and Mott-Schottky (M-S) analysis. The S-doped Cu3Se2, prepared under optimum conditions, exhibited a photocurrent density difference of 880 µA cm−2, which was 6 times greater than for the pristine Cu3Se2 thin film. The results of S-doped Cu3Se2 indicate a negative slope, implying p-type conductivity, and a lower flat band potential value of 0.33 V vs. RHE. Our approach provides a green and cost-effective solution to fabricate S-doped Cu3Se2 thin films for producing hydrogen and oxygen using CBD.

Impact of CVD chemistry on band alignment at the MoS2/SiO2 interface

Reliable knowledge of energy alignment of electronic bands at interfaces of few layered Molybdenum Disulfide (MoS2) is crucial for designing MoS2 based electronic devices. In this work, we have applied internal photoemission spectroscopy (IPE) to characterize this band alignment. MoS2 films grown on SiO2(50 nm)/Siusing two different methods have been analyzed by IPE to determine the energy position of the semiconductor valence band (VB) relative to the reference level of the insulator conduction band (CB). We found that changing the MoS2 growth method from Vapor Phase Reaction (VPR) of MoO3 and sulfur, to Solid Precursor Film (SPF) of sulfurized AHM-NaOH spin coated MoS2 film, results in significant (≈600 meV) enhancement in the electron barrier. Such effects are ascribed to the interaction of hydroxy groups from NaOH and AHM promoters with the SiO2 surface leading to interface dipole modification.

Photoredox Coupling of CO2 Reduction with Benzyl Alcohol Oxidation over Ternary Metal Chalcogenides (ZnmIn2S3+m, m = 1-5) with Regulable Products Selectivity.

Integrating photocatalytic CO2 reduction with selective benzyl alcohol (BA) oxidation in one photoredox reaction system is a promising way for the simultaneous utilization of photogenerated electrons and holes. Herein, ZnmIn2S3+m (m = 1-5) semiconductors (ZnIn2S4, Zn2In2S5, Zn3In2S6, Zn4In2S7, and Zn5In2S8) with various composition faults were synthesized via a simple hydrothermal method and used for effective selective dehydrocoupling of benzyl alcohol into high-value C-C coupling products and reduction of CO2 into syngas under visible light. The absorption edge of ZnmIn2S3+m samples shifted to shorter wavelengths as the atomic ratio of Zn/In was increased. The conduction band and valence band position can be adjusted by changing the Zn/In ratio, resulting in controllable photoredox ability for selective BA oxidation and CO2 reduction. For example, the selectivity of benzaldehyde (BAD) product was reduced from 76% (ZnIn2S4, ZIS1) to 27% (Zn4In2S7, ZIS4), while the selectivity of hydrobenzoin (HB) was increased from 22% to 56%. Additionally, the H2 formation rate on ZIS1 (1.6 mmol/g/h) was 1.6 times higher than that of ZIS4 (1.0 mmol/g/h), and the CO formation rate on ZIS4 (0.32 mmol/g/h) was three times higher than that of ZIS1 (0.13 mmol/g/h), demonstrating that syngas with different H2/CO ratios can be obtained by controlling the Zn/In ratio in ZnmIn2S3+m. This study provides new insights into unveiling the relationship of structure-property of ZnmIn2S3+m layered crystals, which are valuable for implementation in a wide range of environment and energy applications.

Coralloid W18O49@covalent organic frameworks S-scheme heterojunction for high efficiency photocatalytic aerobic oxidation

Reasonably designing and constructing efficient artificial S-mechanism photocatalysts, expanding their application in the field of photocatalytic organic synthesis, have become a hot and challenging topic in the photocatalysis. Herein, a series of coral-like W18O49@TpPa-H (TpPa-H represents COFs generated by the reaction of 1,3,5-triformylphloroglucinol (Tp) and p-phenylenediamine (Pa-H)) composites were successfully prepared by using a simple in-situ encapsulation strategy. Given the internal electric field at the S-scheme interface, W18O49 acts as an oxidative photocatalyst with sufficient positive valence band (VB) position and TpPa-H as a reductive one with enough negative conduction band (CB) position for the efficient amines oxidative coupling to imines. The resulting W18O49@TpPa-H-0.1 hybrid material shows both optimal benzylamine to imine conversion and selectivity exceeding 99 % within 4 h under 10 W 420 nm LED light irradiation, which is 9.9 and 2.8 fold greater than that of W18O49 and TpPa-H, respectively. The photocatalytic activity is even extended to 740 nm. Furthermore, the photocatalytic mechanism research confirmed that a high efficiency S-scheme heterojunction was formed between W18O49 and TpPa-H, and multiple active species, such as ·O2–, 1O2, and h+, synergistically participated in the reaction, imparting its excellent photocatalytic performance. This work may open new avenues for the development of high-efficiency COFs-based S-scheme heterojunction for organic photosynthesis.

The Role of Lattice Defects on the Optical Properties of TiO2 Nanotube Arrays for Synergistic Water Splitting.

In this study, we report a facile one-step chemical method to synthesize reduced titanium dioxide (TiO2) nanotube arrays (NTAs) with point defects. Treatment with NaBH4 introduces oxygen vacancies (OVs) in the TiO2 lattice. Chemical analysis and optical studies indicate that the OV density can be significantly increased by changing reduction time treatment, leading to higher optical transmission of the TiO2 NTAs and retarded carrier recombination in the photoelectrochemical process. A cathodoluminescence (CL) study of reduced TiO2 (TiO2-x) NTAs revealed that OVs contribute significantly to the emission bands in the visible range. It was found that the TiO2 NTAs reduced for a longer duration exhibited a higher concentration of OVs. A typical CL spectrum of TiO2 was deconvoluted to four Gaussian components, assigned to F, F+, and Ti3+ centers. X-ray photoelectron spectroscopy measurements were used to support the change in the surface chemical bonding and electronic valence band position in TiO2. Electron paramagnetic resonance spectra confirmed the presence of OVs in the TiO2-x sample. The prepared TiO2-x NTAs show an enhanced photocurrent for water splitting due to pronounced light absorption in the visible region, enhanced electrical conductivity, and improved charge transportation.

A novel 3D solar evaporator constructed based on the principle of interface evaporation and its application in oil removal and environmental control

It is a challenge to construct devices for producing clean and purified water. In this paper, devices assembled using an aerogel-hydrogel composite and a floating layer were used to produce clean water while purifying water sources. A low-surface-tension polymer and bismuth molybdate were loaded to the surface of a carrier through co-deposition. The contact angle of the constructed superhydrophobic fabric, canvas and felt was 162°, 159° and 160° respectively. Even under the external force of deformation, the beads still quickly left the surface, showing a low adhesion effect. The purification efficiency of the assembled self-floating solar steam generator was 99.82 % and 99.48 % for rhodamine B (Rh B) and methyl orange (MO) respectively, whose mechanical stability and salt suppression capacity were demonstrated through stress–strain curves and photothermal experiments with a high saline concentration (10 wt% NaCl). Through the introduction of bismuth molybdate in the floating layer, not only the roughness increased, but the properties of photodegradation performance were also achieved. Through an active substrate capture test and a band structure analysis, the h+ played a decisive role in the degradation process. The valence and conduction band position of the catalyst were 2.28 eV and −0.35 eV, respectively.

Oxygen vacancy engineered electron structure of porous CexCo3−xO4 nanorods for wide spectrum photocatalytic hydrogen evolution

Development of high-performance semiconductors for photocatalytic hydrogen evolution is a promising solution to solve the current energy crisis. In this work, a porous and oxygen vacancy-enriched CexCo3−xO4-Vo nanorods (CexCo3−xO4-Vo NRs) with adjust electron structure were fabricated by Ce-doping for wide spectrum photocatalytic hydrogen evolution. Because Ce doping regulates the Co3+/Co2+ atomic ratio of Co3O4 nanorods (Co3O4 NRs), resulting in a reduction of oxygen vacancy formation energy and confirmed by electron paramagnetic resonance (EPR) and X-ray photoelectron spectroscopy measurements (XPS) studies. The formation of oxygen vacancy leads to a modification in the positions of conduction band and valence band positions of CexCo3−xO4-Vo NRs. The ultraviolet photoelectron spectroscopy (UPS) spectra results indicate that the generation of oxygen vacancies leads to a more negative Fermi level in CexCo3−xO4-Vo NRs. This result directly results in an enhanced capacity for H+ reduction of CexCo3−xO4-Vo NRs. Density functional theory (DFT) calculations demonstrate that Ce0.15Co2.85O4-Vo NRs have faster electron transfer rates. In addition, the porous rod-like structure endows it abundant electron diffusion pathways, facilitates electrolyte infiltration, and establishes an ideal electrolyte/catalyst contact interface. Among them, Ce0.15Co2.85O4-Vo NRs have the best photocatalytic hydrogen evolution activity (3912.8 μmol g−1), which were 2.2 times more than that of Co3O4 NRs, and an excellent stability also obtained. This work provides a new idea for elements doping Co3O4 NRs to in situ-induced oxygen vacancies for enhanced photocatalytic hydrogen evolution.

Efficient Photocatalytic H2 O2 Production Ability of a Novel Graphitic Carbon Nitride/Carbon Composites under Visible Light.

In the present work, using one-step calcination of a mixture made of potassium hydroxide (KOH), melamine, and microplastics, this work prepares a novel graphitic carbon nitride/carbon (g-C3 N4 /C) composite, which can be employed to photo-catalytically produce hydrogen peroxide (H2 O2 ) at a high rate up to 6.146mmol g-1 h-1 under visible light irradiation. By analyzing the energy band structure of the catalyst, the production of H2 O2 in this system consists of two single-electron reactions. The modification of KOH makes abundant N-vacancies caused by cyano-groups in g-C3 N4 , enhancing the electron absorption ability. Moreover, the introduction of graphitic carbon increases its specific surface area and porosity and improves the adsorption ability of O2 . Simultaneously, their synergism reduces the g-C3 N4 band gap, making both the conduction-band and valence-band positions more negative, showing enhanced reduction ability, lowering the energy barrier for oxygen reduction, and greatly improving the photogeneration performance of H2 O2 .

New insight into the enhanced photocatalytic activity of Al-, C- and Al-C co doped rutile TiO2 photocatalysts

TiO2 has been proven to be the most suitable photocatalytic materials for wide environmental and energy applications because of its suitable valence band and conduction band positions, long-term stability, non-toxicity, cost-effectiveness and strong oxidizing power. Based on the first-principles density functional theory calculations in the framework of density functional theory, the crystal structure, electronic properties, optical properties and photocatalytic activity of photocarriers in Al- doped, C- doped and Al-C co-doped rutile TiO2 systems were investigated. The results show that doping changes the local density and electronic property of rutile TiO2 around the Fermi level. Doping can improve the optical absorption capacity of TiO2 and enlarge its response range to visible light. In addition, the larger of the relative effective mass of photogenerated hole electrons indicates the smaller recombination probability of photogenerated carriers and the higher light catalytic activity. This work will provide some new ideas for understanding the differences in photocatalytic activity between Al- doped, C- doped and Al-C co-doped rutile TiO2, and also provide a new direction for the study of metal and non-metal doped rutile TiO2.

Synergistic effect of excellent carriers separation and efficient high level energy electron utilization on Bi3+-Ce2Ti2O7/ZnIn2S4 heterostructure for photocatalytic hydrogen production

The separation of photogenerated carriers and the efficient utilization of high-level energy electrons (HLEEs) are the key processes for improving the performance of photocatalysts. Herein, Ce2Ti2O7/ZnIn2S4 (CTOZIS) and Bi3+-doped Ce2Ti2O7/ZnIn2S4 (BCTOZIS) photocatalyst were successfully synthesized through hydrothermal method. The photocatalytic hydrogen production of CTOZIS and BCTOZIS was 1233.7 μmol g−1 and 4168.5 μmol g−1 under visible light irradiation (λ ≥ 420 nm) within 5 h, which was 2.3 and 7.6 times than that of pure ZnIn2S4, respectively. X-ray photoelectron spectroscopy, photoluminescence spectroscopy and electrochemical characterization demonstrated that after Bi3+ doping, the electron-hole pairs recombination of BCTOZIS was inhibited, which may be ascribed to the establishment of a Z-scheme heterojunction and the presence of oxygen vacancy and Ce4+/Ce3+ redox center. The doping of Bi3+ resulted in the adjustment of the valence band position of Ce2Ti2O7 from 1.98 V to 1.92 V. This adjustment enabled direct transfer of HLEEs generated in Ce2Ti2O7 to the conduction band of ZnIn2S4 for hydrogen production with a wavelength below 423 nm. The synergistic effect of conventional Z-scheme electron transfer and the unique utilization of HLEEs boosted the photocatalytic performance of BCTOZIS. This study affords an innovative insight for designing visible-light-driven photocatalysts with high photocatalytic activity.

HTL interface engineering in CsPbI3 perovskite photovoltaics

Perovskite photovoltaics are attractive energy conversion device due to > 20% power conversion efficiencies. However, these perovskite semiconductors are highly susceptible to environmental factors such as H2O and O2. To address the device stability, various experimental and simulation investigation on both materials and device level studies were carried out. With the continuous studies and understanding single junction perovskite photovoltaics efficiency crossed 23%. Retaining the fresh device efficiency is the challenging due to afore mentioned reasons. However, to address the stability various strategies were adopted. In this work, various stable and highly interacting HTLs with CsPbI3 were configured in the perovskite photovoltaics to study the output efficiencies. The photovoltaic efficiency of the well configured CsPbI3 device is around ∼ 20% however the hybrid perovskite photovoltaics efficiency is around ∼25%. To obtain the high possible efficiency various device parameters such as semiconductor thickness (t), conduction band position, valence band position, Eg, defect density, Rs, Rsh, device temperature was studied in addition to novel HTLs. Simulation result infer that CuSbS2 shows equivalent/slightly higher PV efficiency (20.56%) as compared with spiroOMeTAD HTL PV. The experimental efficiency and the corresponding device stability will be carried out in the continuation of this work.

The construction of composite hydrogel evaporator with interfacial heating performance and its application in water treatment

To meet the needs of sewage cleaning and clean drinking water, a multifunctional photothermal device is designed in this paper, which mainly includes the non-infiltrating layer of copper stearate, bismuth tungstate and copper oxide composite hydrogel. By improving the synthesis process, sheet-like copper stearate and flower-like bismuth tungstate were prepared, realizing the load of canvas, felt and fabric, with the contact angles reaching 158º, 162º and 161º, respectively. The nonwetting layer has the performance of not only selective oil removal, but also mechanical stability. Through traditional non-infiltrating materials, dyes cannot be degraded, while with the introduction of bismuth tungstate, superhydrophobic materials are given photodegradation properties, thus solving the recovery problem of powder photocatalysts. The photodegradation stability was demonstrated via multiple photodegradation processes by calculating the reaction kinetic coefficient, with a degradation efficiency of greater than 90%. The position of valence (1.9 eV) and conduction (-0.735 eV) band of bismuth tungstate was calculated based on Mott-Schottky curve, DRS and VB-XPS. With the construction of copper oxide composite hydrogel, the mechanical stability was improved and an efficiency of 1.76 kg•m−2•h−1 was obtained. The composite hydrogel device can also be used to treat the aqueous solutions containing metal ions and dyes, which operates stably in aqueous solutions containing 3.5% NaCl without salt crystallization, thus proving the application value of the photothermal device.

Unraveling the Synergy Mechanism between Photocatalysis and Peroxymonosulfate Activation on a Co/Fe Bimetal-Doped Carbon Nitride

Fenton-like catalysis based on peroxymonosulfate (PMS) activation has shown great potential in the treatment of organic wastewater. Heterogeneous Fenton-like catalysts containing transition metal active sites are highly efficient for PMS activation. However, the reduction of oxidized metal active sites was usually not prompt due to the sluggish reaction kinetics, which caused the insufficient redox cycle of the metal active sites and further hampered the catalysis efficiency. Recent studies have shown that the synergy effect between photocatalysis and PMS activation may address the above obstacle and boost overall efficiency. However, a deeper understanding of this synergy effect is still missing, making it difficult to be rationally controlled; thus, a poor synergy effect is frequently reported. Herein, a Co/Fe bimetal-doped graphitic carbon nitride (g-C3N4) was designed representatively through systematical characterization and theoretical calculation, the synergy effect was revealed to be profoundly determined by the competitive role of a hole in the system and the adsorbed metastable PMS* on the catalyst surface, and furthermore, the synergy effect can be rationally manipulated; when the Co/Fe doping ratio is 2.5:2.5, the as-prepared g-C3N4 with a moderate valence band position can endow the catalyst with an optimized photo-Fenton-like synergistic effect and the highest catalytic degradation performance. This work sheds light on the rational design of highly efficient photo-Fenton-like catalysts.

Defect-Induced Modulation of a 2D ZnO/Graphene Heterostructure: Exploring Structural and Electronic Transformations

This paper presents a theoretical study on the effects of selected defects (oxygen vacancies and substitutional FeZn atoms) on the structural and electronic properties of a 2D ZnO/graphene heterostructure. Spin-polarized Hubbard- and dispersion-corrected density functional theory (DFT) was used to optimize the geometrical configurations of the heterostructure and to analyze the equilibrium distance, interlayer distance, adhesion energy, and bond lengths. Charge density difference (CDD) analysis and band structure calculations were also performed to study the electronic properties of the heterostructure. The results show that the presence of defects affects the interlayer distance and adhesion energy, with structures including oxygen vacancies and FeZn substitutional atoms having the strongest interaction with graphene. It is demonstrated that the oxygen vacancies generate localized defect states in the ZnO bandgap and lead to a shift of both valence and conduction band positions, affecting the Schottky barrier. In contrast, Fe dopants induce strong spin polarization and high spin density localized on Fe atoms and their adjacent oxygen neighbors as well as the spin asymmetry of Schottky barriers in 2D ZnO/graphene. This study presents a comprehensive investigation into the effects of graphene on the electronic and adsorption properties of 2D ZnO/graphene heterostructures. The changes in electronic properties induced by oxygen vacancies and Fe dopants can enhance the sensitivity and catalytic activity of the 2D ZnO/graphene system, making it a promising material for sensing and catalytic applications.

Carbon chains modulate carrier transport in tubular graphitic carbon nitride for efficient photocatalytic degradation

In recent years, environmental wastewater has become an increasingly prominent problem, and photocatalytic degradation is one of the effective means to treat waste pollutants. In this study, glycine was embedded in a tubular carbon nitride material with melamine as the parent by a supramolecular self-assembly strategy to prepare carbon chains implanted tubular graphitic carbon nitride (CTCN). The introduction of carbon chains can reduce the formation of hydrogen bonds, which is beneficial to improve the carrier transport efficiency. It can also adjust the valence band position and has better reduction performance. The thin-walled tubular structure formed by supramolecular self-assembly exposes more active sites and shortens the carrier transport distance due to the size effect, which further improves the carrier separation efficiency. The synergistic effect of the two greatly contributes to the photocatalytic performance of the material. The degradation rate of 0.3% CTCN is 8.1 times higher than that of Bulk CN, and 0.3% CTCN exhibits good stability. This solution is beneficial to optimize some existing wastewater treatment methods and has a role in environmental protection.

Highly Selective NH3 Sensor Based on MoS2/WS2 Heterojunction

In this paper, the heterostructure of MoS2/WS2 was prepared by a hydrothermal method; the n-n heterostructure was demonstrated using TEM combined with Mott-Schottky analysis. The valence and conduction band positions were further identified by the XPS valence band spectra. The NH3-sensing properties were assessed at room temperature by changing the mass ratio of the MoS2 and WS2 components. The 50 wt%-MoS2/WS2 sample exhibited the best performance, with a peak response of 23643% to NH3 at a concentration of 500 ppm, a minimum detection limit of 20 ppm, and a fast recovery time of 2.6 s. Furthermore, the composites-based sensors demonstrated an excellent humidity immune property with less than one order of magnitude in the humidity range of 11–95% RH, revealing the practical application value of these sensors. These results suggest that the MoS2/WS2 heterojunction is an intriguing candidate for fabricating NH3 sensors.

Sulfur-vacancy-rich ZnS/CdIn2S4 heterojunction for efficient photocatalytic selective oxidation of toluene to benzaldehyde

The conversion of the volatile organic pollutant to industrially valuable chemicals using photocatalysis is a promising endeavor. Herein, ZnS/CdIn2S4 heterojunction with rich sulfur vacancy was constructed via a simple one-pot method for the selective photocatalytic oxidation of toluene to benzaldehyde. ZnS/CdIn2S4 has a suitable band gap and valence band position, thus possessing a mild oxidation ability to generate benzaldehyde while avoiding excessive oxidation. In addition, the presence of tightly bound contact interfaces and sulfur vacancy in ZnS/CdIn2S4 heterojunction facilitates the rapid separation of photogenerated electron-hole. These characteristics of the heterojunction synergistically promoted the selective photocatalytic oxidation of toluene, resulting in ZnS/CdIn2S4 exhibiting the highest benzaldehyde production rate (1025 μmol g−1 h−1) and the highest conversion rate (13.7%), which were 93.1 and 56.9 times higher than those of ZnS and CdIn2S4, respectively. Furthermore, a possible response mechanism has been suggested based on a series of experiments. This study provides new insights into the combination of volatile organic pollutant degradation and high-value chemicals production.

Research Progress of ZnIn2S4-Based Catalysts for Photocatalytic Overall Water Splitting

Photocatalytic overall water splitting in solar–chemical energy conversion can effectively mitigate environmental pollution and resource depletion. Stable ternary metal indium zinc sulfide (ZnIn2S4) is considered one of the ideal materials for photocatalytic overall water splitting due to its unique electronic and optical properties, as well as suitable conduction and valence band positions for suitable photocatalytic overall water splitting, and it has attracted widespread researcher interest. Herein, we first briefly describe the mechanism of photocatalytic overall water splitting, and then introduce the properties of ZnIn2S4 including crystal structure, energy band structure, as well as the main synthetic methods and morphology. Subsequently, we systematically summarize the research progress of ZnIn2S4-based photocatalysts to achieve overall water splitting through modification methods such as defect engineering, heterostructure construction, and co-catalyst loading. Finally, we provide insights into the prospects and challenges for the overall water splitting of ZnIn2S4-based photocatalysts.

Antibiotics oxytetracycline removal by photocatalyst titanium dioxide and graphitic carbon nitride in aquaculture wastewater

The surge in the use of antibiotics, especially in aquaculture, has led to development of antibiotic resistance genes, which will harm environmental and public health. One of the most commonly used antibiotics in aquaculture is oxytetracycline (OTC). Employing photocatalysis, this study compared OTC degradation efficiency of two different types of common photocatalysts, TiO2 and graphitic carbon nitride (GCN) in terms of their photochemical properties and underlying photocatalytic mechanism. For reference purpose, self-synthesized GCN from urea precursor (GCN-Urea) and commercial GCN (GCN-Commercial) were both examined. OTC adsorption-photocatalysis removal rates in pure OTC solution by TiO2, GCN-Urea and GCN-Commercial were attained at 95%, 60% and 40% respectively. Photochemical properties evaluated included light absorption, band gap, valence and conduction band positions, photoluminescence, cyclic voltammetry, BET surface area and adsorption capability of the photocatalysts. Through the evaluations, this study provides novel insights towards current state-of-the-art heterogeneous photocatalytic processes. The electron-hole recombination examined by photoluminescence is not the key factor influencing the photocatalytic efficacies as commonly discussed. On the contrary, the dominating factors governing the higher OTC degradation efficiency of TiO2 compared to GCN are the high mobility of electrons that leads to high redox capability and the high pollutant-photocatalyst affinity. These claims are proven by 86% and 40% more intense anodic and cathodic cyclic voltammetry curve peaks of TiO2 as compared to both GCNs. OTC also demonstrated 1.7 and 2.3 times higher affinity towards TiO2 than GCN-Urea and GCN-Commercial. OTC removal by TiO2 in real aquaculture wastewater only achieved 50%, due to significant inhibition effect by dissolved solids, dissolved organic matters and high ionic contents in the wastewater.

Strain engineering of type-II C2N/WS2 van der Waals heterojunction for highly enhanced photocatalytic hydrogen evolution

The first-principles calculations demonstrate that the photocatalytic performance of type-II C2N/WS2 van der Waals heterobilayer can be improved to a new and high level by applying weak biaxial strain, with desired band structure, tunable interface charge transfer, superior visible-light absorption, and ideal hydrogen evolution reaction (HER) activity. Tensile strains can largely reduce the energy gap, strengthen the interfacial interactions, and promote the visible-light absorption of C2N/WS2 heterostructure, and even induce a direct band gap of 1.70 eV for overall water splitting at 2% strain. Compressive strains like −2% can upshift the valence band and conduction band positions of the C2N/WS2 bilayer to acquire outstanding redox abilities, and enhance the interface charge transfer and separation by increasing the electrostatic potential drop. More importantly, the cycle between spontaneous H∗ adsorption and energetically favorable H2 release may be realized by dynamic strains between ±2%, maximizing the HER activities of C2N/WS2 heterostructure.