Design of a p–n heterojunction in 0D/3D MoS2/g-C3N4 composite for boosting the efficient separation of photogenerated carriers with enhanced visible-light-driven H2 evolution

Constructing a 0D/3D p–n heterojunction is a feasible strategy for accelerating photo-induced charge separation and promoting photocatalytic H₂ production. In this study, a 0D/3D MoS₂/g-C₃N₄ (0D/3D-MCN) photocatalyst with a p–n heterojunction was prepared via a facile light-assisted deposition procedure, and the 3D spongy-like g-C₃N₄ (3D-CN) was synthesized through simple thermolysis of NH₄Cl and melamine mixture. For comparison, 2D-MoS₂ nanosheets were also embedded in 3D-CN by a solution impregnation method to synthesize a 2D/3D-MCN photocatalyst. As a result, the as-prepared 0D/3D-MCN-3.5% composite containing 3.5 wt% 0D-MoS₂ QDs exhibited the highest photocatalytic H₂ evolution rate of 817.1 μmol h⁻¹ g⁻¹, which was 1.9 and 19.4 times higher than that of 2D/3D-MCN-5% (containing 5 wt% 2D-MoS₂ nanosheets) and 3D-CN, respectively. The results of XPS and electrochemical tests confirmed that a p–n heterojunction was formed in the 0D/3D-MCN-3.5% composite, which could accelerate the electron and hole movement in the opposite direction and retard their recombination; however, it was not found in 2D/3D-MCN-5%. This study revealed the relationship among the morphologies of MoS₂ using g-C₃N₄ as a substrate, the formation of a p–n heterojunction, and the H₂ evolution activity; and provided further insights into fabricating a 3D g-C₃N₄-based photocatalyst with a p–n heterojunction for photocatalytic H₂ evolution.

A 0D/3D p–n heterojunction was formed in the MoS₂/g-C₃N₄ composite, which could promote the separation of electrons and holes efficiently.     

In situ constructed oxygen-vacancy-rich MoO3−x/porous g-C3N4 heterojunction for synergistically enhanced photocatalytic H2 evolution

A simple method was developed for enhanced synergistic photocatalytic hydrogen evolution by in situ constructing of oxygen-vacancy-rich MoO_3−x/porous g-C₃N₄ heterojunctions. Introduction of a MoO_3−x precursor (Mo(OH)₆) solution into g-C₃N₄ nanosheets helped to form a porous structure, and nano-sized oxygen-vacancy-rich MoO_3−xin situ grew and formed a heterojunction with g-C₃N₄, favorable for charge separation and photocatalytic hydrogen evolution (HER). Optimizing the content of the MoO_3−x precursor in the composite leads to a maximum photocatalytic H₂ evolution rate of 4694.3 μmol g⁻¹ h⁻¹, which is approximately 4 times higher of that of pure g-C₃N₄ (1220.1 μmol g⁻¹ h⁻¹). The presence of oxygen vacancies (OVs) could give rise to electron-rich metal sites. High porosity induced more active sites on the pores'' edges. Both synergistically enhanced the photocatalytic HER performance. Our study not only presented a facile method to form nano-sized heterojunctions, but also to introduce more active sites by high porosity and efficient charge separation from OVs.

In situ growth method to construct a nano-sized oxygen-vacancy-rich MoO_3−x/porous g-C₃N₄ heterojunction. MoO_3−x derived OV traps and porous g-C₃N₄ nanosheet derived short migration distance and plentiful edge active sites.     

Bimetallic zeolite-imidazole framework-based heterostructure with enhanced photocatalytic hydrogen production activity

Bimetallic zeolite-imidazole frameworks with controllable flat band position, band gap and hydrogen evolution reaction characteristics were adopted as a photocatalytic hydrogen production catalyst. Furthermore, the g-C₃N₄–MoS₂ 2D–2D surface heterostructure was introduced to the ZnM-ZIF to facilitate the separation as well as utilization efficiency of the photo-exited charge carriers in the ZnM-ZIFs. On the other hand, the ZnM-ZIFs not only inhibited the aggregation of the g-C₃N₄–MoS₂ heterostructure, but also improved the separation and transport efficiency of charge carriers in g-C₃N₄–MoS₂. Consequently, the optimal g-C₃N₄–MoS₂–ZnNi-ZIF exhibited an extraordinary photocatalytic hydrogen evolution activity 214.4, 37.5, and 3.7 times larger than that of the pristine g-C₃N₄, g-C₃N₄–ZnNi-ZIF and g-C₃N₄–MoS₂, respectively, and exhibited a H₂-evolution performance of 77.8 μmol h⁻¹ g⁻¹ under UV-Vis light irradiation coupled with oxidation of H₂O into H₂O₂. This work will furnish a new MOF candidate for photocatalysis and provide insight into better utilization of porous MOF-based heterostructures for hydrogen production from pure water.

The g-C₃N₄-MoS₂ could facilitate the separation as well as utilization efficiency of the photo-generated charge carriers in the ZnM-ZIFs, and hence improved the photocatalytic H₂ production with and without sacrificial agent.     

Fabrication of interlayer β-CD/g-C3N4@MoS2 for highly enhanced photodegradation of glyphosate under simulated sunlight irradiation

Graphitic carbon nitride (g-C₃N₄) has been considered to be a promising metal-free photocatalyst, although the high recombination rate of charge carriers and poor absorption of visible light have limited its applications. In order to overcome these problems, an interlayer composite photocatalyst that comprised β-cyclodextrin (β-CD), oxygen-doped C₃N₄ (O-C₃N₄) and molybdenum disulfide (MoS₂) was successfully constructed for the highly enhanced photodegradation of glyphosate in this study. The structure and morphology, optical properties, and photoelectrochemical properties of the prepared photocatalyst were characterized via a series of characterization techniques. The average fluorescence lifetime of the composite photocatalyst was extended from 6.67 ns to 7.30 ns in comparison with that of g-C₃N₄, which indicated that the composite photocatalyst enhanced the absorption of visible light and also inhibited the recombination of electron–hole pairs. The mass ratio of MoS₂ that corresponded to O-C₃N₄/MoS₂-5 enabled the highest removal rate under simulated sunlight irradiation, which was almost twice that achieved using pure g-C₃N₄. Relative species scavenging experiments revealed that ·O₂⁻ was the main species during the process of photodegradation. Besides, a toxicity test indicated that glyphosate became less toxic or non-toxic after photodegradation. This study provided an effective, feasible and stable photocatalyst driven by simulated sunlight irradiation for the highly enhanced photodegradation of glyphosate.

The fabrication of an interlayer β-CD/g-C₃N₄@MoS₂ composite photocatalyst for highly enhanced photodegradation of glyphosate and a toxicity test.     

Facile synthesis of vacancy-induced 2H-MoS2 nanosheets and defect investigation for supercapacitor application

In this paper, a 2D molybdenum disulfide (MoS₂) nanosheet is prepared via a one-step hydrothermal method as electrode material for supercapacitors. Meanwhile, a series of MoS_2−x nanostructures with sulfur vacancies have been successfully obtained in an Ar/H₂ mixed atmosphere at different annealing temperatures. The prepared materials were characterized by XRD, HR-TEM, Raman and XPS to identify their morphology and crystal properties. MoS_2−x assembled by interconnected nanosheets (MoS_2−x-700) provides a maximum specific capacitance of 143.12 F g⁻¹ at a current density of 1.0 A g⁻¹ with 87.1% of initial capacitance reserved after 5000 cycles. The outstanding performance of the annealed MoS_2−x nanosheets in sodium storage is mainly attributed to the synergistic effect of the unique interconnected structure and the abundant active vacancy generated by the sulfur vacancies. Atomic models of sulfur vacancy defects on the basal plane, Mo-edge and S-edge were established and the electronic properties of MoS_2−x were further evaluated assisted by first principles theory. DFT calculation results show that sulfur vacancy defects can provide additional empty states near the Fermi level and induce unpaired electrons, thus increasing the carrier density and improving electrical conductivity. Our findings in this work provide experimental and theoretical evidence of improving the electrochemical performance of 2H-MoS₂ nanosheets by annealing treatment.

In this paper, a 2D molybdenum disulfide (MoS₂) nanosheet is prepared via a one-step hydrothermal method as electrode material for supercapacitors.     

A dual polymer composite of poly(3-hexylthiophene) and poly(3,4-ethylenedioxythiophene) hybrid surface heterojunction with g-C3N4 for enhanced photocatalytic hydrogen evolution

A surface heterojunction catalyst of g-C₃N₄–PEDOT/P3HT with P3HT and PEDOT as the polymer sensitizer and hole transport pathway is successfully prepared. The as constructed g-C₃N₄–PEDOT/P3HT composite exhibits a photocatalyst H₂ evolution rate up to 427703.3 μmol h⁻¹ g⁻¹ which is 1059 times higher than that of g-C₃N₄, 118 times higher than that of g-C₃N₄–PEDOT with ascorbic acid as sacrificial reagents. What''s more, the g-C₃N₄–PEDOT/P3HT can even show an obviously enhanced photocatalytic H₂ evolution rate which is 6.1 times higher than that of pure g-C₃N₄ in pure water without any sacrificial reagent. Combining the experimental results and molecular dynamic (MD) simulation results, a possible mechanism can be drawn that the existed PEDOT possesses relatively higher hole mobility and can be used as a hole conductor between g-C₃N₄ and P3HT. Then, the photogenerated holes migration can be accelerated by PEDOT from the VB of g-C₃N₄ to the VB of P3HT. All those factors may benefit the synergy among g-C₃N₄, PEDOT and P3HT, which finally facilitates the rapid migration of photoinduced electron–hole pairs and eventually improves the photocatalytic H₂ activity process of g-C₃N₄–PEDOT/P3HT with visible light. The present work may provide useful insights for designing a surface heterojunction composite photocatalyst with high photocatalytic activity for H₂ production.

A surface heterojunction catalyst of g-C₃N₄-PEDOT/P3HT with P3HT and PEDOT as the polymer sensitizer and hole transport pathway is successfully prepared. The as prepared photocatalyst with much improved photocatalytic activity for H₂ production.     

A visible light active,carbon–nitrogen–sulfur co-doped TiO2/g-C3N4 Z-scheme heterojunction as an effective photocatalyst to remove dye pollutants

Heterojunction formation and heteroatom doping could be viewed as promising strategies for constructing composite photocatalysts with high visible light catalytic activity. In this work, we fabricated a carbon, nitrogen and sulfur co-doped TiO₂/g-C₃N₄ (CNS-TiO₂/g-C₃N₄) Z-scheme heterojunction photocatalyst composite via one-step hydrothermal and calcination methods. Compared with pure TiO₂ and g-C₃N₄, the CNS-TiO₂/g-C₃N₄ Z-scheme heterojunction photocatalyst possessed excellent degradation performance under visible light irradiation. Due to the formation of the Z-scheme heterostructure, the utilization rate of the photogenerated electrons–holes generated by the catalyst was increased, which enhanced the catalytic activity. Moreover, the heteroatom doping (C, N and S) could efficiently tailor the band gap of TiO₂ and facilitate electron transition, contributing to enhancing the degradation ability under visible light. The CNS-TiO₂/g-C₃N₄-2 exhibited a superior photocatalytic degradation efficiency (k = 0.069 min⁻¹) for methyl orange dye (MO), which is higher than those of pure TiO₂ (k = 0.001 min⁻¹) and g-C₃N₄ (k = 0.012 min⁻¹), showing excellent photocatalytic activity against organic pollutants.

The CNS-TiO₂/g-C₃N₄ photocatalyst with excellent visible light catalytic activity was successfully manufactured, benefiting from the construction of the Z-scheme heterojunction and the co-doping of heteroatoms (C, N and S).     

Selective CO2 reduction to HCOOH on a Pt/In2O3/g-C3N4 multifunctional visible-photocatalyst

Selective photocatalytic reduction of CO₂ has been regarded as one of the most amazing ways for re-using CO₂. However, its application is still limited by the low CO₂ conversion efficiency. This work developed a novel Pt/In₂O₃/g-C₃N₄ multifunctional catalyst, which exhibited high activity and selectivity to HCOOH during photocatalytic CO₂ reduction under visible light irradiation owing to the synergistic effect between photocatalyst, thermocatalyst, and heterojunctions. Both In₂O₃ and g-C₃N₄ acted as visible photocatalysts, in which porous g-C₃N₄ facilitated H₂ production from water splitting while the In₂O₃ nanosheets embedded in g-C₃N₄ pores favored CO₂ fixation and H adsorption onto the Lewis acid sites. Besides, the In₂O₃/g-C₃N₄ heterojunctions could efficiently inhibit the photoelectron–hole recombination, leading to enhanced quantum efficiency. The Pt could act as a co-catalyst in H₂ production from photocatalytic water splitting and also accelerated electron transfer to inhibit electron–hole recombination and generated a plasma effect. More importantly, the Pt could activate H atoms and CO₂ molecules toward the formation of HCOOH. At normal pressure and room temperature, the TON of HCOOH in CO₂ conversion was 63.1 μmol g⁻¹ h⁻¹ and could reach up to 736.3 μmol g⁻¹ h⁻¹ at 40 atm.

A multifunctional Pt/In₂O₃/g-C₃N₄ catalyst exhibited high activity and selectivity to HCOOH during CO₂ reduction owing to the synergy between visible-light harvesting, CO₂ activation, HER, and photoelectron–hole separation via heterojunctions.     

Structure modulation of g-C3N4 in TiO2{001}/g-C3N4 hetero-structures for boosting photocatalytic hydrogen evolution

Structure design of photocatalysts is highly desirable for taking full advantage of their abilities for H₂ evolution. Herein, the highly-efficient TiO₂{001}/g-C₃N₄ (TCN) heterostructures have been fabricated successfully via an in situ ethanol-thermal method. And the structure of g-C₃N₄ in the TCN heterostructures could be exfoliated from bulk g-C₃N₄ to nanosheets, nanocrystals and quantum dots with the increase of the synthetic temperature. Through detailed characterization, the structural evolution of g-C₃N₄ could be attributed to the enhanced temperature of the ethanol-thermal treatment with the shear effects of HF acid. As expected, the optimal TCN-2 heterostructure shows excellent photocatalytic H₂ evolution efficiency (1.78 mmol h⁻¹ g⁻¹) under visible-light irradiation. Except for the formed built-in electric field, the significantly enhanced photocatalytic activity of TCN-2 could be ascribed to the enhanced crystallinity of TiO₂{001} nanosheets and the formed g-C₃N₄ nanocrystals with large surface area, which could extend the visible light absorption, and expedite the transfer of photo-generated charge carriers further. Our work could provide guidance on designing TCN heterostructures with the desired structure for highly-efficient photocatalytic water splitting.

The structure of g-C₃N₄ in the prepared TiO₂{001}/g-C₃N₄ hetero-structures could be modulated from BCN to CN-NS, CN-NC or CN-QD by tuning the synthetic temperature.     

One-step scalable synthesis of honeycomb-like g-C3N4 with broad sub-bandgap absorption for superior visible-light-driven photocatalytic hydrogen evolution

Integration of a nanostructure design with a sub-bandgap has shown great promise in enhancing the photocatalytic H₂ production activity of g-C₃N₄via facilitating the separation of photogenerated charges while simultaneously increasing the active sites and light harvesting ability. However, the development of a synthetic route to generate an ordered g-C₃N₄ structure with remarkable sub-bandgap absorption via a scalable and economic approach is challenging. Herein, we report the preparation of a honeycomb-like structured g-C₃N₄ with broad oxygen sub-bandgap absorption (denoted as HOCN) via a scalable one-pot copolymerization process using oxamide as the modelling agent and oxygen doping source. The morphology and sub-bandgap position can be tailored by controlling the oxamide to dicyandiamide ratio. All HOCN samples exhibit remarkable enhancement of photocatalytic H₂ production activity due to the synergistic effect between the sub-bandgap and honeycomb structure, which results in strong light absorption extending up to 1000 nm, fast separation of photogenerated charge carriers, and rich photocatalytic reaction sites. In particular, HOCN4 exhibits a remarkable photocatalytic H₂ production rate of 1140 μmol h⁻¹ g⁻¹ under visible light irradiation (>420 nm), which is more than 13.9 times faster than the production rate of pristine g-C₃N₄. Moreover, even under longer wavelength light irradiation (i.e., >500 and >800 nm), HOCN4 still exhibits a high H₂ production rate of 477 and 91 μmol h⁻¹ g⁻¹, respectively. In addition, HOCN4 possesses an apparent quantum yield (AQY) of 4.32% at 420 nm and 0.12% at 800 nm. These results confirm that the proposed synthesis strategy allow for scalable production of g-C₃N₄ with an ordered nanostructure via electronic modulation, which is beneficial for its practical application in photocatalytic H₂ production.

Integration of a nanostructure design with a sub-bandgap enhances the photocatalytic H₂ production activity of g-C₃N₄via facilitating separation of photogenerated charges while simultaneously increasing the active sites and light harvesting ability.     

Scalable nanohybrids of graphitic carbon nitride and layered NiCo hydroxide for high supercapacitive performance

The limited number of edge nitrogen atoms and low intrinsic electrical conductivity hinder the supercapacitive energy storage applications of the nitrogen-rich graphitic carbon nitride (g-C₃N₄). In this study, a novel graphitic carbon nitride/NiCo-layered double hydroxide (CNLDH), a two-dimensional nanohybrid, is prepared by a simple hydrothermal synthesis. The homogeneous interpolation of g-C₃N₄ nanosheets into NiCo LDH stacked nanosheets effectively increases the overall performances of the g-C₃N₄/NiCo LDH nanohybrid. The improved morphology of the nanohybrid electrode upon the addition of g-C₃N₄ to the NiCo LDH yields a specific capacity of 183.43 mA h g⁻¹ in 6 M KOH at 1 A g⁻¹, higher than those of bare g-C₃N₄ (20.89 mA h g⁻¹) and NiCo LDH (95.92 mA h g⁻¹) electrodes. The excellent supercapacitive performance of the CNLDH nanohybrid is complemented by its low internal resistance, excellent rate capability, and large cycling lifetime. Furthermore, the hybrid supercapacitor is assembled using CNLDH 0.1 as a positive electrode and activated carbon (AC) as a negative electrode. The hybrid supercapacitor device of CNLDH 0.1//AC shows the maximum specific capacity of 37.44 mA h g⁻¹ at 1 A g⁻¹ with remarkable energy density, power density and good cycling performance. This confirms that the CNLDH 0.1 nanohybrid is an excellent electrode material for supercapacitor applications.

A two dimensional CNLDH 0.1 nanohybrid supercapacitor electrode prepared by simple hydrothermal hybridization of g-C₃N₄ and NiCO LDH shows the maximum specific capacity of 183.43 mA h g⁻¹ with remarkable electrochemical performance.     

Construction of a double heterojunction between graphite carbon nitride and anatase TiO2 with co-exposed (101) and (001) faces for enhanced photocatalytic degradation

This study aimed to promote the separation of photogenerated carriers and improve the redox performance of graphite carbon nitride (g-C₃N₄) by synthesizing a double-heterojunction-structure photocatalyst, g-C₃N₄/(101)-(001)-TiO₂, through the solvothermal method. The photocatalyst comprised a Z-system formed from g-C₃N₄ and the (101) plane of TiO₂, as well as a surface heterojunction formed from the (101) and (001) planes of TiO₂. The results showed that g-C₃N₄/(101)-(001)-TiO₂ had strong photocatalytic activity and stable performance in the photodegradation of paracetamol. The active species ·O₂⁻ and ·OH were found to play important roles in the photocatalytic degradation of paracetamol through a radical-quenching experiment. The charge-transfer mechanism was also described in detail. Overall, this work provided a new strategy for the Z-system heterojunction and opened up the application of this structure in the degradation of organic pollutants.

A double-heterojunction-structure photocatalyst g-C₃N₄/(101)-(001)-TiO₂ with Z-system and surface heterojunction, was synthesized, which can effectively promote the separation of photogenerated e⁻–h⁺ pairs and the degradation of organic pollutants.     

Evaluation of dual layered photoanode for enhancement of visible-light-driven applications

Ternary structures consisting of hollow g-C₃N₄ nanofibers/MoS₂/sulfur, nitrogen-doped graphene and bulk g-C₃N₄ (TCN) were designed as a dual layered film and fabricated using a spin-coating method. The first ternary structures were spin-coated on fluorine-doped tin oxide (FTO) glass, followed by spin-coating of g-C₃N₄ film to form dual layers. We characterized the microstructural morphologies, chemical composition/bonding and optical properties of the dual layered film and observed significantly reduced recombination rates of photo-induced electron–hole pairs due to effective separation of the charge carriers. We tested methylene blue (MB) photodegradation and observed remarkable MB degradation by the dual layered film over 5 hours, with a kinetic rate constant of 1.24 × 10⁻³ min⁻¹, which is about four times faster than that of bare TCN film. Furthermore, we estimated the H₂ evolution of the dual layered film to be 44.9 μmol over 5 hours, and carried out stable recycling over 45 hours under visible irradiation. Due to the lower electrochemical impedance spectroscopy (EIS) resistance value of the dual layered film (∼50 ohm cm²) compared to the TCN film, the ternary structures and bulk g-C₃N₄ film were well-connected as a heterojunction, reducing the resistance at the interface between the film and the electrolyte. These results indicate that the effective separation of the photo-induced electron–hole pairs using the dual layered film dramatically improved its photo-response ability under visible light irradiation.

Ternary structures consisting of hollow g-C₃N₄ nanofibers/MoS₂/sulfur, nitrogen-doped graphene and bulk g-C₃N₄ (TCN) were designed as a dual layered film and fabricated using a spin-coating method.     

g-C3N4/CuO and g-C3N4/Co3O4 nanohybrid structures as efficient electrode materials in symmetric supercapacitors

Metal oxide dispersed graphitic carbon nitride hybrid nanocomposites (g-C₃N₄/CuO and g-C₃N₄/Co₃O₄) were prepared via a direct precipitation method. The materials were used as an electrode material in symmetric supercapacitors. The g-C₃N₄/Co₃O₄ electrode based device exhibited a specific capacitance of 201 F g⁻¹ which is substantially higher than those using g-C₃N₄/CuO (95 F g⁻¹) and bare g-C₃N₄ electrodes (72 F g⁻¹). At a constant power density of 1 kW kg⁻¹, the energy density given by g-C₃N₄/Co₃O₄ and g-C₃N₄/CuO devices is 27.9 W h kg⁻¹ and 13.2 W h kg⁻¹ respectively. The enhancement of the electrochemical performance in the hybrid material is attributed to the pseudo capacitive nature of the metal oxide nanoparticles incorporated in the g-C₃N₄ matrix.

Comparison of electrochemical performance of symmetric supercapacitors based on g-C₃N₄/CuO and g-C₃N₄/Co₃O₄ electrodes.     

Highly dispersed NiS2 quantum dots as a promising cocatalyst bridged by acetylene black significantly improved the photocatalytic H2 evolution performance of g-C3N4 nanosheets

In this work, ternary nanocomposite (CNs–AB/NiS₂) as a novel efficient H₂ evolution photocatalyst without the use of noble metals was successfully synthesized by depositing acetylene black (AB) and ultra-fine NiS₂ nanoparticles on the surface of CNs (g-C₃N₄) through ultrasonic dispersion and chemical vapor deposition methods, respectively. It was revealed that the loaded AB and NiS₂ nanoparticles have significantly improved the photocatalytic H₂ evolution efficiency of the CNs by improving the photogenerated electron–hole pair separation, visible light absorption and hydrogen evolution kinetics. Besides acting as a cocatalyst, AB served as a conductive electron bridge between CNs and NiS₂, which accelerated the effective transfer of electrons from CNs to NiS₂ and improved the H₂ evolution kinetics of the NiS₂ cocatalyst. The H₂ evolution experiments revealed that the ternary photocatalyst CNs–AB/NiS₂10 displayed a H₂ evolution rate of up to 2434.85 μmoL g⁻¹ h⁻¹, which was a 1.41 times enhancement compared to that of the binary composite CNs–NiS₂10 and was 12.43 times higher than that of the pure CNs. Moreover, the ternary photocatalyst CNs–AB/NiS₂10 not only exhibited excellent photocatalytic activity and stability in the tests, but provided a novel idea for the development of high-efficiency catalysts free of noble metals as well.

We have successfully designed and synthesised a series of binary and ternary photocatalysts without noble metal cocatalysts for H₂ generation by dispersing NiS₂ and acetylene black nanoparticles on ultra-thin g-C₃N₄ nanosheets.     

Tuning of structural and optical properties with enhanced catalytic activity in chemically synthesized Co-doped MoS2 nanosheets

Molybdenum disulfide (MoS₂) nanosheets, due to having a highly active nature, being low cost and having unique physical and chemical properties, have shown their efficacy in the catalytic reduction of nitroarenes. Doping of transition metal ions in molybdenum disulfide (MoS₂) nanosheets is a well-known strategy to enhance their catalytic efficiency for the reduction of nitroarenes, however, finding the optimum dopant amount is still a subject of ongoing research. Herein, we have synthesized few-layered cobalt (Co) doped MoS₂ nanosheets with different cobalt content (2%, 4%, 6% and 8%) through the solvothermal approach, taking sodium molybdate dihydrate (Na₂MoO₄·2H₂O), thiourea (CH₄N₂S) and cobalt acetate tetrahydrate [Co(CH₃COO)₂·4H₂O] as precursors and their catalytic performance has been affirmed by monitoring the reduction of p-nitrophenol by NaBH₄ in real time using UV-visible absorption spectroscopy. The 6% Co doped MoS₂ nanosheets have exhibited superior catalytic activity with a pseudo-first order rate constant of 3.03 × 10⁻³ s⁻¹ attributed to the abundant defects in the active edge sites having a dominant metallic 1T phase with Co ion activated defective basal planes, sulphur (S) edges, synergistic structural and electronic modulation between MoS₂ and Co ions and enhanced electron transfer assisted through redox cycling in the active sites. An attempt has also been made to study the manipulation of structural and optical properties with cobalt doping in MoS₂ nanosheets to establish a correlation between the catalytic efficiency and dopant content. This study demonstrates that proper tuning of Co doping in MoS₂ nanosheets paves the way in searching for a potential alternative of a noble metal catalyst for the catalytic reduction of nitroarenes.

The optimal cobalt (6% Co) doped MoS₂ catalyst has shown the highest catalytic activity due to the presence of abundant defects in the active edge sites, having dominant metallic 1T phase with Co ion activated defective basal planes.     

Construction of a non-enzymatic electrochemical sensor based on graphitic carbon nitride nanosheets for sensitive detection of procalcitonin

In this study, we established a label free and ultrasensitive electrochemical sensor based on graphitic nitride nanosheets (g-C₃N₄ NS) for procalcitonin (PCT) detection. Firstly, an easy-to-prepare and well-conducting g-C₃N₄ NS was synthesized. Next the g-C₃N₄ NS was immobilized on the electrode surface by π–π stacking, and further used to anchor the specific recognition peptide (PP). The surface morphology and structure after g-C₃N₄ NS and PP modification was characterized by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and electrochemistry. The sensing property of this sensor was evaluated by differential pulse voltammetry (DPV) and showed a detection sensitivity with a dynamic range from 0.15 to 11.7 fg mL⁻¹ with a low limit of detection (LOD) of 0.11 fg mL⁻¹. Besides, the electrochemical biosensor was successfully used to detect PCT in human serum samples, and the results suggest its potential use in clinical application.

A simple and ultra-sensitive electrochemical biosensor based on graphitic carbon nitride nanosheets (g-C₃N₄ NS) was developed for the detection of PCT. This sensor presented excellent sensing performance and demonstrates potential for clinical application.     

A Cu2+-doped two-dimensional material-based heterojunction photoelectrode: application for highly sensitive photoelectrochemical detection of hydrogen sulfide

In this work, on the basis of a Cu²⁺-doped two-dimensional material-based heterojunction photoelectrode, a novel anodic photoelectrochemical (PEC) sensing platform was constructed for highly sensitive detection of endogenous H₂S. Briefly, with g-C₃N₄ and TiO₂ as representative materials, the sensor was fabricated by modifying g-C₃N₄/TiO₂ nanorod arrays (NAs) onto the surface of fluorine-doped tin oxide (FTO) and then doping Cu²⁺ as a Cu_xS (x = 1, 2) precursor. After the binding of S²⁻ with surface-attached Cu²⁺, the signal was quenched owing to the in situ generation of Cu_xS which offers trapping sites to hinder generation of photocurrent signals. Since the photocurrent inhibition was intimately associated with the concentration of S²⁻, a highly sensitive PEC biosensor was fabricated for H₂S detection. More importantly, the proposed sensing platform showed the enormous potential of g-C₃N₄/TiO₂ NAs for further development of PEC bioanalysis, which may serve as a common basis for other semiconductor applications and stimulates the exploration of numerous high-performance nanocomposites.

In this work, on the basis of a Cu²⁺-doped two-dimensional material-based heterojunction photoelectrode, a novel anodic photoelectrochemical (PEC) sensing platform was constructed for highly sensitive detection of endogenous H₂S.     

Enhanced photocatalytic hydrogen evolution and ammonia sensitivity of double-heterojunction g-C3N4/TiO2/CuO

The performance of semiconductor photocatalysts has been limited by rapid electron–hole recombination. One strategy to overcome this problem is to construct a heterojunction structure to improve the survival rate of electrons. In this context, a novel g-C₃N₄/TiO₂/CuO double-heterojunction photocatalyst was developed and characterized. Its photocatalytic activity for hydrogen production from water–methanol photocatalytic reforming was explored. Methanol is always used to eliminate semiconductor holes. The g-C₃N₄/TiO₂/CuO double-heterojunction photocatalyst with a narrow bandgap of ∼1.38 eV presented excellent photocatalytic activity for hydrogen evolution (97.48 μmol (g h)⁻¹) under visible light irradiation. Compared with g-C₃N₄/TiO₂ and CuO/TiO₂, the photocatalytic activity of g-C₃N₄/TiO₂/CuO for hydrogen production was increased approximately 7.6 times and 1.8 times, respectively. Below 240 °C, the sensitivity of g-C₃N₄/TiO₂/CuO to ammonia was approximately 90% and 46% higher than that of g-C₃N₄/TiO₂ and CuO/TiO₂, respectively. The enhancement of the photocatalytic activity and gas sensing properties of the g-C₃N₄/TiO₂/CuO composite resulted from the close interface contact established by the double heterostructure. The trajectory of electrons in the double heterojunction conformed to the S-scheme. UV-vis, PL, and transient photocurrent characterization showed that the double heterostructure effectively inhibited the recombination of e⁻/h⁺ pairs and enhanced the migration of photogenerated electrons.

The trajectory of electrons in the g-C3N4/TiO2/CuO double-heterojunction conforms to the S-scheme.     

Synthesis of a UiO-66/g-C3N4 composite using terephthalic acid obtained from waste plastic for the photocatalytic degradation of the chemical warfare agent simulant,methyl paraoxon

In our study, Zr-based UiO-66 (Zr) was synthesized using terephthalic acid obtained from waste plastic. Thereafter, UiO-66/g-C₃N₄ composites were prepared by the solvothermal method, and their photocatalytic activity in the photodegradation of the chemical warfare agent simulant, dimethyl 4-nitrophenyl phosphate (DMNP), was evaluated. The as-synthesized UiO-66/g-C₃N₄ exhibited a high surface area (1440 m² g⁻¹) and a high capillary volume (1.49 cm³ g⁻¹). The UiO-66/g-C₃N₄ samples absorbed a visible light band with bandgap energies of 2.13–2.88 eV. The as-synthesized UiO-66/g-C₃N₄ composites exhibited highly efficient degradation of DMNP with a short half-life (t_1/2 of 2.17 min) at pH 7 under visible light irradiation. The trapping experiments confirmed that the h⁺ and ˙O₂⁻ radicals played an important role in the photocatalytic degradation of DMNP. The UiO-66/g-C₃N₄ catalyst simultaneously performed two processes: the hydrolysis and photocatalytic oxidation of DMNP in water. During irradiation, a p–n heterojunction between UiO-66 and g-C₃N₄ restricted the recombination of photogenerated electrons and holes, resulting in the enhancement in the degradation rate of DMNP.

UiO-66/g-C₃N₄ with a high surface area (1440 m² g⁻¹) and a high capillary volume (1.49 cm³ g⁻¹) exhibited highly efficient degradation of dimethyl 4-nitrophenyl phosphate with t_1/2 = 2.17 min.