Rapid high-temperature hydrothermal post treatment on graphitic carbon nitride for enhanced photocatalytic H2 evolution

Awakening n-π* electron transition in structurally distorted g-C3N4 nanosheets via hexamethylenetetramine-involved supercritical CO2 treatment towards efficient photocatalytic H2 production

Graphitic carbon nitride (g-C3N4) has been regarded as highly potential photocatalyst for solar energy utilization. However, the restricted absorption of visible light for pristine g-C3N4 significantly limits the solar-light-driven chemical reaction efficiency. Herein, structurally distorted g-C3N4 nanosheets with awakened n-π* electron transition were successfully synthesized through hexamethylenetetramine (HMTA)-involved supercritical CO2 (scCO2) treatment and following pyrolysis of melamine precursor. ScCO2 treatment was conductive to homogeneously dissoving melamine precursor and HMTA, and then the modification by HMTA with three-dimensional structure changed the g-C3N4 photocatalyst from a symmetrical planar structure to an asymmetrical non-planar structure. The resulting awakened n-π* electron transition in structurally distorted g-C3N4 nanosheets greatly extended the photoresponse range of g-C3N4 and increased the amount of catalytically active π electrons. Moreover, the unique distorted structure of g-C3N4 enhanced photogenerated charge carriers separation and provided sufficient reactive sites for photocatalytic H2 production. Consequently, the structurally distorted g-C3N4 nanosheets exhibited enhanced photocatalytic H2 production performance, which was up to 6.4 times that of pristine g-C3N4. This work presents a promising scCO2 strategy towards precursor treatment to regulate the microstructure of g-C3N4, and provides valuable guidance to obtain efficient g-C3N4 photocatalyst by microstructure engineering.

Janus structure hydrogels: recent advances in synthetic strategies, biomedical microstructure and (bio)applications

Janus structure hydrogels (JSHs) are novel materials. Their primary fabrication methods and various applications have been widely reported. JSHs are primarily composed of Janus particles (JNPs) and polysaccharide components. They exhibit two distinct physical or chemical properties, generating intriguing characteristics due to their asymmetric structure. Normally, one side (adhesive interface) is predominantly constituted of polysaccharide components, primarily serving excellent adhesion. On the other side (functional surface), they integrate diverse functionalities, concurrently performing a plethora of synergistic functions. In the biomedical field, JSHs are widely applied in anti-adhesion, drug delivery, wound healing, and other areas. It also exhibits functions in seawater desalination and motion sensing. Thus, JSHs hold broad prospects for applications, and they possess significant research value in nanotechnology, environmental science, healthcare, and other fields. Additionally, this article proposes the challenges and future work facing these fields.

Supercritical CH3OH-Triggered Isotype Heterojunction and Groups in g-C3N4 for Enhanced Photocatalytic H2 Evolution

The structure tuning of bulk graphitic carbon nitride (g-C3N4) is a critical way to promote the charge carriers dynamics for enhancing photocatalytic H2-evolution activity. Exploring feasible post-treatment strategies can lead to effective structure tuning, but it still remains a great challenge. Herein, a supercritical CH3OH (ScMeOH) post-treatment strategy (250-300 °C, 8.1-11.8 MPa) is developed for the structure tuning of bulk g-C3N4. This strategy presented advantages of time-saving (less than 10 min), high yield (over 80%), and scalability due to the enhanced mass transfer and high reactivity of ScMeOH. During the ScMeOH post-treatment process, CH3OH molecules diffused into the interlayers of g-C3N4 and subsequently participated in N-methylation and hydroxylation reactions with the intralayers, resulting in a partial phase transformation from g-C3N4 into carbon nitride with a poly(heptazine imide)-like structure (Q-PHI) as well as abundant methyl and hydroxyl groups. The modified g-C3N4 showed enhanced photocatalytic activity with an H2-evolution rate 7.2 times that of pristine g-C3N4, which was attributed to the synergistic effects of the g-C3N4/Q-PHI isotype heterojunction construction, group modulation, and surface area increase. This work presents a post-treatment strategy for structure tuning of bulk g-C3N4 and serves as a case for the application of supercritical fluid technology in photocatalyst synthesis.

One-Step Synthesis of Transition Metal Dichalcogenide Quantum Dots Using Only Alcohol Solvents for Indoor-Light Photocatalytic Antibacterial Activity

In this study, we report a one-step direct synthesis of molybdenum disulfide (MoS₂) and tungsten disulfide (WS₂) quantum dots (QDs) through a solvothermal reaction using only alcohol solvents and efficient Escherichia coli (E. coli) decompositions as photocatalytic antibacterial agents under visible light irradiation. The solvothermal reaction gives the scission of molybdenum-sulfur (Mo-S) and tungsten-sulfur (W-S) bonding during the synthesis of MoS₂ and WS₂ QDs. Using only alcohol solvent does not require a residue purification process necessary for metal intercalation. As the number of the CH₃ groups of alcohol solvents among ethyl, isopropyl, and tert(t)-butyl alcohols increases, the dispersibility of MoS₂/WS₂ increases. The CH₃ groups of alcohols minimize the surface energy, leading to the effective exfoliation and disintegration of the bulk under heat and pressure. The bulky t-butyl alcohol with the highest number of methyl groups shows the highest exfoliation and yield. MoS₂ QDs with a lateral size of about 2.5 nm and WS₂ QDs of about 10 nm are prepared, exhibiting a strong blue luminescence under 365 nm ultraviolet (UV) light irradiation. Their heights are 0.68-3 and 0.72-5 nm, corresponding to a few layers of MoS₂ and WS₂, respectively. They offer a highly efficient performance in sterilizing E. coli as the visible-light-driven photocatalyst.

Augmented photocatalytic degradation of Acetaminophen using hydrothermally treated g-C3N4 and persulfate under LED irradiation

Photocatalytic degradation of organic pollutants in water using graphitic carbon nitride and persulfate under visible light (g-C₃N₄/PS system) has been studied. Here, we demonstrate augmentation of photocatalytic degradation of Acetaminophen (AAP) using hydrothermally treated g-C₃N₄ and PS under 400 nm LED irradiation (HT-g-C₃N₄/PS system). A pseudo-first-order rate constant (k_obs, 0.328 min^-1) for degradation of AAP using HT-g-C₃N₄/PS system was determined to be 15 times higher compared to g-C₃N₄/PS system (k_obs, 0.022 min^-1). HT-g-C₃N₄ showed a higher surface area (81 m²/g) than g-C₃N₄ (21 m²/g). Photocurrent response for HT-g-C₃N₄ was higher (1.5 times) than g-C₃N₄. Moreover, Nyquist plot semicircle for HT-g-C₃N₄ was smaller compared to g-C₃N₄. These results confirm effective photoelectron-hole separation and charge-transfer in HT-g-C₃N₄ compared to g-C₃N₄. AAP degradation using HT-g-C₃N₄/PS system was significantly inhibited with O2.- and h⁺ scavengers compared to ¹O_2,SO4.- and HO. scavengers. ESR results revealed O2.- formation in HT-g-C₃N₄/PS system. Moreover, photocurrent measurements reveal AAP oxidation by h⁺ of HT-g-C₃N₄ was effective than g-C₃N₄. HT-g-C₃N₄ was reused for five cycles in HT-g-C₃N₄/PS system. Augmented photocatalytic degradation of AAP by HT-g-C₃N₄/PS system compared to g-C₃N₄/PS is attributed to effective photoelectron hole separation of HT-g-C₃N₄ that generates O2.- and h⁺ for oxidation of pollutant. Importantly, electrical energy per order (E_EO) was 7.2 kWh m^-3 order^-1. k_obs for degradation of AAP in simulated groundwater and tap water were determined as 0.029 and 0.035 min^-1, respectively. Degradation intermediates of AAP were proposed. AAP ecotoxicity against marine bacteria Aliivibrio fischeri was completely removed after treatment by HT-g-C₃N₄/PS system.

Size effect of ruthenium nanoparticles on water cracking properties with different crystal planes for boosting electrocatalytic hydrogen evolution

Small size ruthenium (Ru) nanoparticles have shown remarkable potential for electrocatalytic hydrogen evolution reaction (HER). Nevertheless, the complicated preparation and relatively low activity of small size Ru nanoparticles are two key challenges. In this work, carbon nanotubes supported Ru nanoparticles catalysts (cnts@NC-Ru t °C) with different sizes were prepared via using the combination of L-3,4-dihydroxyphenylalanine (l-dopa) self-polymerization oxidation reaction and different high temperature annealing to study the variation of particle activity with size. Electrochemical test results showed that the optimized cnts@NC-Ru 700 °C catalyst exhibited a very low overpotential at 10 mA/cm² (21 mV) and tafel slope of 34.93 mV/dec when the mass loading of precious metal per unit area was merely 12.11 μg/cm² that surpassed most recently reported high-performance Ru based catalyst. The results of density functional theory (DFT) calculation showed that small Ru nanoparticles had abundant active sites, and the H₂O dissociation on small Ru nanoparticles (110) surface is quite easy than other surfaces, while (111) surface of small Ru nanoparticles is beneficial for Tafel step of HER. The synergy between (110) and (111) surfaces on the Ru cluster contributes to its outstanding HER performance. This study provides a novel design idea in promoting the preparation method and uncovering the reason of high activity of small size Ru nanoparticles.

Deciphering the Superior Electronic Transmission Induced by the Li-N Ligand Pairs Boosted Photocatalytic Hydrogen Evolution

Atomic level decoration route is designated as one of the attractive methods to regulate both the charge density and band structure of photocatalysts. Moreover, to enable more efficient separation and transport of photocarriers, the construction of novel active sites can enhance both the reactivity and electrical conductivity of the crystal. Herein, an Li-N ligand is constructed via co-doping lithium and nitrogen atoms into ZnIn₂ S₄ lattice, which achieves a promoted photocatalytic H₂ evolution at 9737 µmol g^-1 h^-1 . The existence of Li-N ligand pairs and the behaviors of photocarriers on L₄₀ N₅ ZIS are determined systematically, which also provides a unique insight into the mechanism of the improved photocarrier migration rate. With the introduction of Li-N dual sites, the vacancy form of ZnIn₂ S₄ has changed and the photocatalytic stability is significantly improved. Interestingly, the change of charge density around Li-N ligand in ZnIn₂ S₄ is determined by theoretical simulations, as well as the regulated energy barrier of photocatalytic water splitting caused by Li-N dual sites, which act as both adsorption site for H₂ O and stronger reactive sites. This work helps to extend the understanding of ZnIn₂ S₄ and offers a fresh perspective for the creation of a Li-N co-doped photocatalyst.

Architecture and Kinetic Studies of Photocatalytic H2O2 Generation and H2 Evolution through Regulation of Spatial Charge Transfer via Z-Scheme Path over a (001) Facet Engineered TiO2@MXene/B-g-C3N4 Ternary Hybrid

Spatial charge separation and migration are the critical shortcomings dominating the core energy conversion corridors of photocatalytic systems. Here, a biomimetic multi-interfacial architecture providing strong coupled interaction and rapid charge transmission for photostable and competent photocatalytic H2O2 production and H2 evolution is proposed. The triple-hybrid all-solid-state Z-scheme system was formed with the (001) facet exposed TiO2 nanosheets derived from MXene layers and B-g-C3N4 nanosheets (M/(001)TiO2@BCN) through an electrostatic self-assembly strategy with intimate electronic interaction due to Ti orbital modulation and proper stacking among the hybrids. The metallic and highly conductive MXene layers act as solid state electron mediators in the Z-scheme heterojunction that promote electron-hole separation and migration efficiency. Specifically, the MTBCN-12.5 composite provides optimum yield of H2O2 up to 1480.1 μmol h-1 g-1 and a H2 evolution rate of 408.4 μmol h-1 (with ACE 6.7%), which are 4 and 20 fold greater than the pristine BCN, respectively. The enhanced photocatalytic performance is systematically identified by the increased surface area, higher cathodic and anodic current densities of -1.01 and 2.27 mA cm-2, delayed charge recombination as supported by PL and EIS measurement, and excellent photostability. The Z-scheme charge transfer mechanism is validated by time-resolved photoluminescence (TRPL) analysis, cyclic voltametric analysis, and the radical trapping experiment as detected by PL analysis. This research marks a substantial advancement and establishes the foundation for future design ideas in accelerating charge transfer.

N-doped rutile TiO2 nanorod@g-C3N4 core/shell S-scheme heterojunctions for boosting CO2 photoreduction activity

A novel core/shell structure composed of N-doped rutile TiO2@g-C3N4 (NT@CNx) with an S-scheme heterojunction is successfully synthesized. The S-scheme heterojunction optimizes the electrochemical property and redox ability of the NT@CNx composite.

Uniform-embeddable-distributed Ni3S2 cocatalyst inside and outside a sheet-like ZnIn2S4 photocatalyst for boosting photocatalytic hydrogen evolution

The rational cocatalyst design is considered a significant route to boost the solar-energy conversion efficiency for photocatalytic H₂ generation. However, the traditional cocatalyst-loading on the surface of a photocatalyst easily leads to scarce exposed active sites induced by the agglomeration of cocatalysts and a hindrance of the light absorption of the photocatalyst, thus significantly limiting the enhancement of the photocatalytic H₂-generation performance. Herein, a new concept of uniform-embeddable-distributed cocatalysts is put forward. Consequently, uniform-embeddable-distributed cocatalysts of Ni₃S₂ were designed and constructed inside and outside of the nanosheet-like ZnIn₂S₄ photocatalyst to form a Ni₃S₂/ZnIn₂S₄ binary system (UEDNiS/ZIS). The unique uniform-embeddable-distributed Ni₃S₂ cocatalyst (UEDNiS) could provide abundant exposed active sites, facilitate the spatial separation and ordered transfer of charges inside and outside of ZnIn₂S₄ nanosheets, and reduce the hydrogen-adsorption free energy for photocatalytic H₂-generation reactions. As a result, UEDNiS/ZIS exhibited a high photocatalytic H₂-generation rate of 60 μmol h^-1 under visible-light irradiation, almost 7.8 and 2.8 times higher than pristine ZnIn₂S₄ and the traditional surface-loaded Ni₃S₂/ZnIn₂S₄ (TSLNiS/ZIS), respectively. This work represents a new cocatalyst-design approach to realize high-efficiency hydrogen evolution in binary heterostructured photocatalytic systems.

Nanosheets of In2S3/S-C3N4-Dots for Solar Water-Splitting in Saline Water

Hydrogen generation from splitting of water under the photoelectrochemical (PEC) pathway is considered as the most promising strategy for covering the upcoming fuel crisis by taking care of all environmental issues. In this context, In₂S₃ can be explored as it is a visible light-active semiconductor with an appropriate band alignment with the water redox potential. Herein, In₂S₃ nanosheets are developed by the chemical method. The nanosheets of In₂S₃ absorb high visible light due to the manifold inside scattering and reflection. The PEC activity of In₂S₃ is enhanced because of the increase in the light absorbance of the materials. In the present work, at 1.18 V versus RHE in 3.5 wt % NaCl, a maximum 2.07 mA/cm² photocurrent density can be achieved by In₂S₃ nanosheets. However, In₂S₃ suffers strongly due to photo-corrosion. To improve the efficacy of the In₂S₃ nanosheets in saline water, the charge-carrier transportation ability of In₂S₃ is aimed to increase by decorating S-C₃N₄-dots on In₂S₃. The heterostructure of type-II is developed by sensitization of S-C₃N₄-dots on In₂S₃. It increases both the transportation of charge carriers as well as separation. In the heterostructure, the transient decay time (τ) increases, which indicates a decrease in photogenerated charge-carrier recombination. S-C₃N₄-dots also act as an optical antenna and increase the range of visible light absorbance of In₂S₃. The heterostructure can generate ∼2.38-fold higher photocurrent density of 1.18 V versus RHE in 3.5 wt % NaCl. The photoconversion efficiency of the heterostructure is 0.88% at 0.95 V versus RHE. The nanosheets of In₂S₃ and In₂S₃/S-C₃N₄-dots are stable, and photocurrent density is measured up to 2700 s under continuous back-illumination conditions.

Optimization of PEC and photocathodic protection performance of TiO2/CuInS2heterojunction photoanodes

The establishment of heterojunction is a powerful strategy to enhance the photoresponse performance of photoanode. Here, TiO₂/CuInS₂(T/CIS) composites were prepared via a two-step hydrothermal method, and their morphologies were controlled by adjusting the reaction time. The absorption spectra show that CuInS₂can significantly improve the absorption of visible light. The T/CIS2 (2 h reaction time) photoanode exhibited the most outstanding photoelectrochemical (PEC) performance, with a photocurrent density of 168% that of the pure TiO₂photoanode. Under simulated sunlight, this photoanode can supply a protective photocurrent of 0.49 mA cm^-2and a protective voltage of 0.36 V to stainless steel (304ss), which are about 4 and 2 times those of the TiO₂sample. The enhancement in the photocathodic protection performance is attributed to enlarged visible light absorbance and higher charge separation rate. This study demonstrates that the TiO₂/CuInS₂photoanode is a promising candidate for application in photoinduced cathodic protection of metallic materials.

Furfural Influences Hydrogen Evolution and Energy Conversion in Photo-Fermentation by Rhodobacter capsulatus

Furfural, as a typical byproduct produced during the hydrolysis of lignocellulose biomass, is harmful to the photo fermentation hydrogen production. In this work, the effects of furfural on the photo fermentation hydrogen production by Rhodobacter capsulatus using glucose as substrate were investigated. The characteristics of cell growth, hydrogen production, and fermentation end-products with the addition of different concentrations of furfural (0–20 mM) were studied. The results showed that furfural negatively affected the maximum hydrogen production rate and total hydrogen yield. The maximum hydrogen yield of 2.59 ± 0.13 mol-H2/mol-glucose was obtained without furfural. However, 5 mM furfural showed a 40% increase in cell concentration. Furfural in high concentrations can favor the overproduction and accumulation of inhibitive end-products. Further analysis of energy conversion efficiency showed that most of the energy in the substrate was underused and unconverted when the furfural concentration was high. The maximum glucose consumption (93%) was achieved without furfural, while it dramatically declined to 7% with 20 mM furfural addition. The index of half-maximal inhibitory concentration was calculated as 13.40 mM. Moreover, the possible metabolic pathway of furfural and glucose was discussed.

Localized surface plasmon resonance effect enhanced Cu/TiO2 core–shell catalyst for boosting CO2 hydrogenation reaction

Inexpensive and nontoxic Cu/TiO2 catalysts based on the LSPR effect for boosting the CO2 hydrogenation reaction.

Size-dependent Al-doped SrTiO3 affecting solar-driven overall water splitting

The equilibrium relationship between the charge transfer and gas evolution capacities of reasonable size Al-STO nanoparticles induces the balance point of HER and OER half-reactions.

Hematite nanoparticles decorated nitrogen-doped reduced graphene oxide/graphitic carbon nitride multifunctional heterostructure photocatalyst towards environmental applications

The carcinogenic heavy metals and aromatic organic compounds linger as wastewater pollutants implying great menace to the ecological balance. To solve these environmental pollution problems, the photocatalytic process is an...