Novel PtPd alloy nanoparticle-decorated g-C3N4 nanosheets with enhanced photocatalytic activity for H2 evolution under visible light irradiation

PtPd bimetallic alloy nanoparticle (NP)-modified graphitic carbon nitride (g-C₃N₄) nanosheet photocatalysts were synthesized via chemical deposition precipitation. Characterization of the photocatalytic H₂ evolution of the g-C₃N₄ nanosheets shows that it was significantly enhanced when PtPd alloy NPs were introduced as a co-catalyst. The 0.2 wt% PtPd/g-C₃N₄ composite photocatalyst gave a maximum H₂ production rate of 1600.8 μmol g^–1 h^–1. Furthermore, when K₂HPO₄ was added to the reaction system, the H₂ production rate increased to 2885.0 μmol g^–1 h^–1. The PtPd/g-C₃N₄ photocatalyst showed satisfactory photocatalytic stability and was able to maintain most of its photocatalytic activity after four experimental photocatalytic cycles. In addition, a possible mechanism for the enhanced photocatalytic activity was proposed and verified by various photoelectric techniques. These results demonstrate that the synergistic effect between PtPd and g-C₃N₄ helps to greatly improve the photocatalytic activity of the composite photocatalyst.     

Hydrogen production and photocatalytic activity of g-C3N4/Co-MOF (ZIF-67) nanocomposite under visible light irradiation

Herein, cobalt (Co)-based metal–organic zeolitic imidazole frameworks (ZIF-67) coupled with g-C₃N₄ nanosheets synthesized via a simple microwave irradiation method. SEM, TEM and HR-TEM results showed that ZIF-67 were uniformly dispersed on g-C₃N₄ surfaces and had a rhombic dodecahedron shape. The photocatalytic properties of g-C₃N₄/ZIF-67 nanocomposite were evaluated by photocatalytic dye degradation of crystal violet (CV), 4-chlorophenol (4-CP) and photocatalytic hydrogen (H₂) production. In presence of visible light illumination, the photocatalytic dye results showed that 95% CV degradation and 53% 4-CP degradation within 80 min. The H₂ production of the g-C₃N₄/ZIF-67 composite was 2084 μmol g⁻¹, which is 3.84 folds greater than that of bare g-C₃N₄ (541 μmol g⁻¹).     

HKUST-1 Derived Hollow C-Cu2−xS Nanotube/g-C3N4 Composites for Visible-Light CO2 Photoreduction with H2O Vapor

As the main component of syngas, reducing CO₂ to CO with high selectivity through photocatalysis could provide a sustainable way to alleviate energy shortage issues. Developing a photocatalytic system with low cost and high performance that is environmentally friendly is the ultimate goal towards CO₂ photoreduction. Herein, an efficient and economic three-component heterojunction photocatalyst is designed and fabricated for converting CO₂ to CO in the absence of organic sacrificial agents. The heterojunction is made of Cu_2−xS nanotubes coated with a carbon layer (C-Cu_2−xS) and g-C₃N₄. By using the classical MOF material HKUST-1 as a precursor, hollow tubular-like metal sulfides (C-Cu_2−xS) with carbon coating were synthesized and further loaded on g-C₃N₄, forming a three-component heterojunction C-Cu_2−xS@g-C₃N₄. The carbon coat in C-Cu_2−xS@g-C₃N₄ acts as an electron reservoir, which facilitates electron–hole pair separation. The optimized C-Cu_2−xS@g-C₃N₄ acted as a photocatalyst in CO₂ reduction with a high reactivity of 1062.6 μmol g⁻¹ and selectivity of 97 %. Compared with bare g-C₃N₄ (158.4 μmol g⁻¹) and C-Cu_2−xS, the reactivity is nearly 7 and 23-fold enhanced and this CO generation rate is higher than most of the reported Cu₂S or g-C₃N₄ composites under similar conditions. The prominent activity may result from enhanced light adsorption and effective charge separation. This work might open up an alternative method for the design and fabrication of high-performance and low-cost photocatalysts for efficiently and durably converting CO₂ to CO with high selectivity.     

A novel P-doped and NCDs loaded g-C3N4 with enhanced charges separation for photocatalytic hydrogen evolution

Graphite carbon nitride(g-C₃N₄) is a promising non-metal photocatalyst for photocatalytic hydrogen production, but its performance is still limited due to sluggish charges separation and low utilization of light.In this work, P-doped and N-doped carbon dots(NCDs) supported g-C₃N₄were successfully prepared via hydrothermal and polymerization reactions. The sub-bandgap formed by P-doping enhances the utilization of visible light, and the high electron de...     

Vinylene-Linked Covalent Organic Frameworks (COFs) with Symmetry-Tuned Polarity and Photocatalytic Activity

The polarity of a semiconducting molecule affects its intrinsic photophysical properties, which can be tuned by varying the molecular geometry. Herein, we developed a D_3h-symmetric tricyanomesitylene as a new monomer which could be reticulated into a vinylene-linked covalent organic framework (g-C₅₄N₆-COF) via Knoevenagel condensation with another D_3h-symmetric monomer 2,4,6-tris(4′-formyl-biphenyl-4-yl)-1,3,5-triazine. Replacing tricyanomesitylene with a C_2v-symmetric 3,5-dicyano-2,4,6-trimethylpyridine gave a less-symmetric vinylene-linked COF (g-C₅₂N₆-COF). The octupolar conjugated characters of g-C₅₄N₆-COF were reflected in its scarce solvatochromic effects either in ground or excited states, and endowed it with more promising semiconducting behavior as compared with g-C₅₂N₆-COF, such as enhanced light-harvesting and excellent photo-induced charge generation and separation. Along with the matched energy level, g-C₅₄N₆-COF enabled the two-half reactions of photocatalytic water splitting with an average O₂ evolution rate of 51.0 μmol h⁻¹ g⁻¹ and H₂ evolution rate of 2518.9 μmol h⁻¹ g⁻¹. Such values are among the highest of state-of-the-art COF photocatalysts.     

Integrating non-precious-metal cocatalyst Ni3N with g-C3N4 for enhanced photocatalytic H2 production in water under visible-light irradiation

Photocatalytic H₂ production via water splitting in a noble-metal-free photocatalytic system has attracted much attention in recent years. In this study, noble-metal-free Ni₃N was used as an active cocatalyst to enhance the activity of g-C₃N₄ for photocatalytic H₂ production under visible-light irradiation (λ > 420 nm). The characterization results indicated that Ni₃N nanoparticles were successfully loaded onto the g-C₃N₄, which accelerated the separation and transfer of photogenerated electrons and resulted in enhanced photocatalytic H₂ evolution under visible-light irradiation. The hydrogen evolution rate reached ～305.4 μmol h^?1 g^?1, which is about three times higher than that of pristine g-C₃N₄, and the apparent quantum yield (AQY) was ～0.45% at λ = 420. Furthermore, the Ni₃N/g-C₃N₄ photocatalyst showed no obvious decrease in the hydrogen production rate, even after five cycles under visible-light irradiation. Finally, a possible photocatalytic hydrogen evolution mechanism for the Ni₃N/g-C₃N₄ system is proposed.     

Non-Interacting Ni and Fe Dual-Atom Pair Sites in N-Doped Carbon Catalysts for Efficient Concentrating Solar-Driven Photothermal CO2 Reduction

Solar-to-chemical energy conversion under weak solar irradiation is generally difficult to meet the heat demand of CO₂ reduction. Herein, a new concentrated solar-driven photothermal system coupling a dual-metal single-atom catalyst (DSAC) with adjacent Ni−N₄ and Fe−N₄ pair sites is designed for boosting gas-solid CO₂ reduction with H₂O under simulated solar irradiation, even under ambient sunlight. As expected, the (Ni, Fe)−N−C DSAC exhibits a superior photothermal catalytic performance for CO₂ reduction to CO (86.16 μmol g⁻¹ h⁻¹), CH₄ (135.35 μmol g⁻¹ h⁻¹) and CH₃OH (59.81 μmol g⁻¹ h⁻¹), which are equivalent to 1.70-fold, 1.27-fold and 1.23-fold higher than those of the Fe−N−C catalyst, respectively. Based on theoretical simulations, the Fermi level and d-band center of Fe atom is efficiently regulated in non-interacting Ni and Fe dual-atom pair sites with electronic interaction through electron orbital hybridization on (Ni, Fe)−N−C DSAC. Crucially, the distance between adjacent Ni and Fe atoms of the Ni−N−N−Fe configuration means that the additional Ni atom as a new active site contributes to the main *COOH and *HCO₃ dissociation to optimize the corresponding energy barriers in the reaction process, leading to specific dual reaction pathways (COOH and HCO₃ pathways) for solar-driven photothermal CO₂ reduction to initial CO production.     

Bifunctional copper modified graphitic carbon nitride catalysts for efficient tetracycline removal: Synergy of adsorption and photocatalytic degradation

In order to efficiently remove tetracycline in wastewater through the synergistic effect of adsorption and photocatalytic degradation, a series of novel composite materials (Cu doped g-C₃N₄) were synthesized by two-pot hydrothermal method. It was found that the composite materials with optimized ratio (Cu/CN-1) displayed outstanding adsorption and photocatalytic performance as compared with pure g-C₃N₄ photocatalyst. The removal efficiency of tetracycline (TC, 50 mg/L) reached almost 99% within 30 min by Cu/CN-1 through the synergy of adsorption and photocatalysis under visible-light irradiation, which was the highest removal efficiency ever reported. The adsorption kinetics and isotherms of TC on the Cu/CN-1 were well fitted with the pseudo-second-order kinetic model and Langmuir model, respectively. Moreover, it was confirmed that the main effective reactive groups were O₂⁻ and h⁺ in photocatalytic process. The Cu/CN-1 exhibited high stability and excellent reusability after five cycle experiments. Finally, the mechanism of synergy between Cu and g-C₃N₄ was proposed: on the one hand, the decoration of Cu particles significantly increased the adsorption sites of Cu/CN-1 to tetracycline, on the other hand, the modification of Cu particles effectively inhibits charge recombination and broadens the visible light absorption range of the photocatalyst.This study provided a promising photocatalyst to be used for TC removal in the actual wastewater.     

A Metal-Organic-Framework-Derived g-C3N4/α-Fe2O3 Hybrid for Enhanced Visible-Light-Driven Photocatalytic Hydrogen Evolution

As one of the most efficient systems for photocatalytic hydrogen evolution, the Z-Scheme system, consisting of different semiconductors with a reversible donor–acceptor pair, has attracted great attention. Considering the non-toxicity and low cost of photocatalysts, a series of g-C₃N₄/α-Fe₂O₃ hybrids were rationally constructed based on the Z-Scheme mechanism for the first time, using a metal-organic framework template approach that can fine tune the compositions and properties of the hybrids. An optimized hybrid, g-C₃N₄/α-Fe₂O₃-2, exhibited prominent photocatalytic water splitting performance with a visible light response. Under irradiation of visible light (λ>420 nm), the hybrid shows a high durability and superior hydrogen production rate of 2066.2 μmol g⁻¹ h⁻¹ from water splitting, which is approximately three times greater than that of bulk g-C₃N₄ because of the effective separation of photo-excited charge carriers by two narrow band gap semiconductors, tightly coupled with the Z-Scheme structural feature.     

Defects Promote Ultrafast Charge Separation in Graphitic Carbon Nitride for Enhanced Visible-Light-Driven CO2 Reduction Activity

Fundamental photocatalytic limitations of solar CO₂ reduction remain due to low efficiency, serious charge recombination, and short lifetime of catalysts. Herein, two-dimensional graphitic carbon nitride nanosheets with nitrogen vacancies (g-C₃N_x) located at both three-coordinate N atoms and uncondensed terminal NH_x species were prepared by one-step tartaric acid-assistant thermal polymerization of dicyandiamide. Transient absorption spectra revealed that the defects in g-C₃N₄ act as trapped states of charges to result in prolonged lifetimes of photoexcited charge carriers. Time-resolved photoluminescence spectroscopy revealed that the faster decay of charges is due to the decreased interlayer stacking distance in g-C₃N_x in favor of hopping transition and mobility of charge carriers to the surface of the material. Owing to the synergic virtues of strong visible-light absorption, large surface area, and efficient charge separation, the g-C₃N_x nanosheets with negligible loss after 15 h of photocatalysis exhibited a CO evolution rate of 56.9 μmol g⁻¹ h⁻¹ under visible-light irradiation, which is roughly eight times higher than that of pristine g-C₃N₄. This work presents the role of defects in modulating light absorption and charge separation, which opens an avenue to robust solar-energy conversion performance.     

Surface molecular imprinting on g-C3N4 photooxidative nanozyme for improved colorimetric biosensing

Graphitic carbon nitride (g-C₃N₄), as a visible-light-active organic semiconductor, has attracted growing attentions in photocatalysis and photoluminescence-based biosensing. Here, we demonstrated the intrinsic photooxidase activity of g-C₃N₄ and then surface molecular imprinting on g-C₃N₄ nanozymes was achieved for improved biosensing. Upon blue LED irradiation, the g-C₃N₄ exhibited superior enzymatic activity for oxidation of chromogenic substrate like 3,3′,5,5′-tetramethylbenzidine (TMB) without destructive H₂O₂. The oxidation was mainly ascribed to O₂⁻ that was generated during light irradiation. The surface molecular imprinting on g-C₃N₄ can lead to an over 1000-fold alleviation in matrix-interference from serum samples, 4-fold improved enzymatic activity as well as enhanced substrate specificity comparing with bare g-C₃N₄ during colorimetric sensing. Also, the MIP-g-C₃N₄ possesses a high affinity to TMB with a K_m value of only 22 μmol/L, much lower than other comment nanozymes like AuNPs, Fe₃O₄ NPs, etc. It was successfully applied for detection of cysteine in serum sample with satisfactory recoveries.     

Surface plasmon resonance excited electron induction greatly extends H2 evolution and pollutant degradation activity of g-C3N4 under visible light irradiation

Energy crises and environmental pollution have sparked tremendous research work to handle their impacts. Herein, we fabricated Au/g-C₃N₄ nanocomposites to produce H₂ and degrade 2,4-dichlorophenol (2,4-DCP) under visible light and at different wavelengths. Interestingly, the optimized photocatalyst generated 114 μmol H₂ and degraded 25% 2,4-DCP in 1 hr as compared with 10 μmol H₂ generation and 8% 2,4-DCP degradation by pure g-C₃N₄. This improvement is credited to the extended light absorption and improved charge induction from gold to g-C₃N₄ even at 590 nm as confirmed from photoluminescence, surface photovoltage, and photoelectrochemical study of the samples. Moreover, the surface catalytic property of g-C₃N₄ was much improved after loading a proper amount of gold nanoparticles. We hope that this technique to photosensitize semiconductors with noble metal nanoparticles may provide a feasible way to construct surface plasmon resonance-assisted photocatalysts to cope with energy crises and environmental pollution simultaneously.     

ZnO-based ternary nanocomposite for decolorization of methylene blue by photocatalytic dynamic membrane

In this article, novel Ag–ZnO/g-C₃N₄/GO ternary nanocomposites were prepared via co-precipitation method by 1%w Ag, 50% w g-C₃N₄, 10% w GO concentration and applied in dynamic membranes. The characteristics of Ag–ZnO/g-C₃N₄/GO nanocomposite were evaluated by various techniques such as X-ray diffraction, field emission scanning electron microscopy, energy dispersive X-ray map, transmission electron microscopy, X-ray photoelectron spectroscopy, photocatalyst. The photocatalytic degradation of methylene blue was investigated under visible light. The photocatalytic efficiency of 93.43% for methylene blue degradation was obtained for Ag–ZnO/g-C₃N₄/GO nanocomposite after 50 min of irradiation, which was remarkably higher than that of pure ZnO, bare g-C₃N₄, Ag–ZnO, and Ag–ZnO/g-C₃N₄ at the same irradiation time. Likewise, in self-forming and pre-coated membranes, ternary nanocomposites can play a vital role in the membrane surface properties, as well as their decolorization performance. The rejection of methylene blue was 30% in pure polyethersulfone membrane, while the photocatalytic degradation of methylene blue in Ag–ZnO/g-C₃N₄/GO nanocomposites was 88.46% and 98.86% after 10 and 15 min of irradiation in both self-forming and pre-coated dynamic membranes, respectively. Experimental results show that the dynamic membrane possesses a higher ability for degradation of MB in a shorter period of time than the static system.     

Cascaded electron transition proved by femto-second transient absorption spectroscopy for enhanced photocatalysis hydrogen generation

Regulating flow direction of photo-excited electrons from interior to active sites in surface is critical to enhance the photocatalytic performance. Herein, photoinduced chemical reduction process was utilized to pinpoint deposit CdS and NiS nanodots sequentially onto g-C₃N₄ nanosheets. The resulted hybrid composite NiS/CdS/g-C₃N₄ was much more active under visible light, and eventually boosted the hydrogen evolution rate of 3015 μmol g^?1 h^?1, to be 2.4 folds better than that of g-C₃N₄. Because of the relative low content of CdS (around 3.0 wt%), the enhanced activity is due to the favoring band overlapping and promoting charge separation rather than increasing light absorption. Femto-second time-resolved transient absorption spectroscopy (fs-TAS) clearly reveals that the photo-excited electrons are from g-C₃N₄, and then migrate unidirectionally to CdS and finally to NiS, which is caused by the precisely regulate the position of CdS and NiS on g-C₃N₄ surface. This study elucidates the electron transfer kinetics and processes in multi-component system and affords a new avenue to construct stable photocatalysts with high activity.     

Single‐Site Active Cobalt‐Based Photocatalyst with a Long Carrier Lifetime for Spontaneous Overall Water Splitting

An active and stable photocatalyst to directly split water is desirable for solar‐energy conversion. However, it is difficult to accomplish overall water splitting without sacrificial electron donors. Herein, we demonstrate a strategy via constructing a single site to simultaneously promote charge separation and catalytic activity for robust overall water splitting. A single Co₁‐P₄ site confined on g‐C₃N₄ nanosheets was prepared by a facile phosphidation method, and identified by electron microscopy and X‐ray absorption spectroscopy. This coordinatively unsaturated Co site can effectively suppress charge recombination and prolong carrier lifetime by about 20 times relative to pristine g‐C₃N₄, and boost water molecular adsorption and activation for oxygen evolution. This single‐site photocatalyst exhibits steady and high water splitting activity with H₂ evolution rate up to 410.3 μmol h⁻¹ g⁻¹, and quantum efficiency as high as 2.2 % at 500 nm.     

Advantageous Interfacial Effects of AgPd/g-C3N4 for Photocatalytic Hydrogen Evolution: Electronic Structure and H2O Dissociation

Bimetallic AgPd nanoparticles have been synthesized before, but the interfacial electronic effects of AgPd on the photocatalytic performance have been investigated less. In this work, the results of hydrogen evolution suggest that the bimetallic AgPd/g-C₃N₄ sample has superior activity to Ag/g-C₃N₄ and Pd/g-C₃N₄ photocatalysts. The UV/Vis diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy, CO adsorption diffuse reflectance FTIR spectroscopy, and FTIR results demonstrate that in the AgPd/g-C₃N₄, the surface electronic structures of Pd and Ag are changed, which is beneficial for faster photogenerated electron transfer and greater H₂O molecule adsorption. In situ ESR spectra suggest that, under visible light irradiation, there is more H₂O dissociation to radical species on the AgPd/g-C₃N₄ photocatalyst. Furthermore, DFT calculations confirm the interfacial electronic effects of AgPd/g-C₃N₄, that is, Pd^δ−⋅⋅⋅Ag^δ+, and the activation energy of H₂O molecule dissociation on AgPd/g-C₃N₄ is the lowest, which is the main contributor to the enhanced photocatalytic H₂ evolution.     

Cu、C共负载ZnO光催化剂固氮性能及机理

为提高ZnO催化剂光催化固氮性能,克服其光生电子-空穴复合率高、可见光响应能力差以及易光腐蚀等缺点,本研究采用Cu、C共负载方式对ZnO催化剂进行改性(以下简称CuCZ催化剂)。结果显示,CuCZ-3%(Cu占ZnO质量的3%)催化剂的光催化固氮速率最大,达到4.96 mmol·g_cat^-1·h^-1,为ZnO(0.612 mmol·g_cat^-1·h^-1)的8.10倍、CZnO(C负载ZnO,3.00 mmol·g_cat^-1·h^-1)的1.65倍。通过X射线衍射(XRD)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)、高分辨透射电子显微镜(HRTEM)、X射线光电子能谱(XPS)、紫外可见漫反射光谱(UV-Vis DRS)、光致发光光谱(PL)以及电化学阻抗谱(EIS)对CuCZ催化剂进行表征以探究其光催化固氮效果提高的机理。结果表明,Cu、C共负载产生的界面电荷转移机制和C的"电子桥梁...     

Fabrication of novel Ag/g-C3N4 electrode for resveratrol sensors

Ag/g-C₃N₄ is fabricated and used as an electrode for determining trans-resveratrol concentration. The compositional and structural characteristics of the as-fabricated Ag/g-C₃N₄ are studied through X-ray diffraction, transmission electron microscopy, and energy dispersive spectroscopy. Additionally, the electrochemical behavior of Ag/g-C₃N₄ is investigated using cyclic voltammetry. According to the experimental results, 1 wt%Ag/g-C₃N₄ exhibits an oxidation peak at 0.48 V, with a low detection limit (1.88 × 10⁻⁷ M) and satisfactory correlation coefficient (0.9975), suggesting that the proposed Ag/g-C₃N₄ electrode can be successfully used for detecting trans-resveratrol.     

In situ hydrothermal growth of ZnO/g-C3N4 nanoflowers coated solid-phase microextraction fibers coupled with GC-MS for determination of pesticides residues

In this paper, Zinc oxide (ZnO) hybridized with graphite-like C₃N₄ (ZnO/g-C₃N₄) nanoflowers based solid phase microextraction (SPME) coating was prepared on fiber using in situ hydrothermal growth method for gas chromatographic -mass spectrum (GC- MS) separation and analysis target analytes in complex matrixes for the first time. The proposed hybrid ZnO/g-C₃N₄ fiber exhibited wide linearity for the pesticide residues in range of 0.003–5.0 ng mL⁻¹. The limits of detection (LOD) were 0.001–0.0025 ng mL⁻¹. The relative standard deviation (RSD) for three replicate extractions using one fiber was ranged from 2.3% to 7.6%. The fiber to fiber RSD was 5.3–11.3% (n = 3). This method was successfully used for simultaneous determination of nine pesticide residues in cucumber, pear, Green tea and Minjiang water with satisfactory recoveries of 79.1–103.5%. These results indicated that the ZnO/g-C₃N₄ composite provided a promising alternative in sample pretreatment and analysis.