热剥离g-C_(3)N_(4)纳米片的合成及光催化性能研究

以三聚氰胺为前驱体,合成块状g-C_(3)N_(4)(CN),再经简单的热剥离技术,成功制备多孔g-C_(3)N_(4)纳米片(CN-S)光催化剂。系统研究了不同热剥离时间对CN-S光催化还原Cr(VI)性能的影响。结果表明:经4 h热剥离后获得的样品CN-S(4h)比表面积和孔体积分别为191.88m^(2)·g^(-1)和1.109cm^(3)·g^(-1),而CN的比表面积和孔体积分别是7.82m^(2)·g^(-1)和0.092cm^(3)·g^(-1),说明热剥离可显著提升材料比表面积和孔体积,增加表面有效活性位点,延长可见光在其内部的多重散射,缩短光生电子-空穴对从材料内部迁移至表面的传输距离。此外,热剥离处理形成的碳空位可增强光生载流子分离效率。由此CN-S(4h)光催化还原Cr(VI)的效率达到99.0%。

Enhanced visible light photocatalytic H_2 production over Z-scheme g-C_3N_4 nansheets/WO_3 nanorods nanocomposites loaded with Ni(OH)_x cocatalysts

Novel WO3/g-C3N4/Ni（OH）x hybrids have been successfully synthesized by a two-step strategy of high temperature calcination and in situ photodeposition.Their photocatalytic performance was investigated using TEOA as a hole scavenger under visible light irradiation.The loading of WO3 and Ni（OH）x cocatalysts boosted the photocatalytic H2 evolution efficiency of g-C3N4.WO3/g-C3N4/Ni（OH）x with 20 wt%defective WO3 and 4.8 wt%Ni（OH）x showed the highest hydrogen production rate of 576 μmol/（g·h）,which was 5.7,10.8 and 230 times higher than those of g-C3N4/4.8 wt%Ni（OH）x,20 wt%WO3/C3N4 and g-C3N4 photocatalysts,respectively.The remarkably enhanced H2 evolution performance was ascribed to the combination effects of the Z-scheme heterojunction（WO3/g-C3N4） and loaded cocatalysts（Ni（OH）x）,which effectively inhibited the recombination of the photoexcited electron-hole pairs of g-C3N4 and improved both H2 evolution and TEOA oxidation kinetics.The electron spin resonance spectra of ·O2^- and ·OH radicals provided evidence for the Z-scheme charge separation mechanism.The loading of easily available Ni（OH）x cocatalysts on the Z-scheme WO3/g-C3N4 nanocomposites provided insights into constructing a robust multiple-heterojunction material for photocatalytic applications.

g-C3N4/ZnO复合光催化剂降解污染物的研究进展

ZnO具有光催化活性强、稳定性高等优点,然而,ZnO禁带宽度大,只能吸收紫外光,太阳能利用率低;且其光生电子易与空穴复合,量子效率低。g-C3N4是一种窄带隙半导体,与ZnO复合形成异质结,不仅可以提高太阳光利用率,而且能加快载流子转移,提高光催化性能。通过文献研究综述了g-C3N4/ZnO复合光催化剂的四种复合形式,以及g-C3N4、ZnO与其他物质复合而成的三元、四元复合材料,并对g-C3N4/ZnO复合光催化剂的未来发展方向进行了展望。

Pd/g-C_3N_4对水中2,4-二氯酚的催化加氢脱氯研究

分别采用光沉积法和浸渍法制备了载钯石墨相氮化碳催化剂(Pd/g-C3N4-PD和Pd/g-C3N4-IMP),并对其进行了电感耦合等离子体发射光谱(ICP-AES)、X射线衍射(XRD)、透射电镜(TEM)和Zeta电位的表征.结果表明,不同载钯量Pd/g-C3N4-PD的等电点均在p H 2.3左右;Pd/g-C3N4-PD表面Pd粒子分散均匀,且Pd粒径小于Pd/g-C3N4-IMP.分别将Pd/g-C3N4-PD和Pd/g-C3N4-IMP用于2,4-二氯酚的催化加氢脱氯研究,Pd/g-C3N4-PD的催化脱氯效果明显优于Pd/g-C3N4-IMP.低p H值利于2,4-二氯酚的催化加氢脱氯过程,但不利于保持催化剂的稳定性.

MoS_(2)/g-C_(3)N_(4)复合光催化剂的构建及其可见光催化性能研究

本研究通过水热合成法和超声法成功构建MoS_(2)/g-C_(3)N_(4)复合型光催化剂。通过X射线粉末衍射(XRD)、扫描电子显微镜(SEM)、红外光谱(IR)以及紫外-可见吸收光谱(UV-Vis)表征技术对复合型催化剂的物理化学特性进行分析。以光催化降解罗丹明B(RhB)为探针反应,探究可见光下不同质量比的MoS_(2)/g-C_(3)N_(4)复合型光催化剂对RhB光催化降解性能的影响。实验结果表明,当MoS_(2)负载量为30%,光催化降解80 min时,10 mg/L的RhB溶液的降解率为96.7%。MoS_(2)/g-C_(3)N_(4)复合催化剂相比于纯的g-C_(3)N_(4),MoS_(2)降解RhB的效果有显著地提高。光催化降解性能的提升归因于两半导体间MoS_(2)和g-C_(3)N_(4)异质结界面构筑,有效地抑制光生电子(e^(-))和空穴(h^(+))的复合,从而提高复合型光催化剂MoS_(2)/g-C_(3)N_(4)的光催化性能。

Sulfur-doped g-C3N4/TiO2 S-scheme heterojunction photocatalyst for Congo Red photodegradation

Constructing step-scheme(S-scheme)heterojunctions has been confirmed as a promising strategy for enhancing the photocatalytic activity of composite materials.In this work,a series of sulfur-doped g-C3N4(SCN)/TiO2 S-scheme photocatalysts were synthesized using electrospinning and calcination methods.The as-prepared SCN/TiO2 composites showed superior photocatalytic performance than pure TiO2 and SCN in the photocatalytic degradation of Congo Red(CR)aqueous solution.The significant enhancement in photocatalytic activity benefited not only from the 1D well-distributed nanostructure,but also from the S-scheme heterojunction.Furthermore,the XPS analyses and DFT calculations demonstrated that electrons were transferred from SCN to TiO2 across the interface of the SCN/TiO2 composites.The built-in electric field,band edge bending,and Coulomb interaction synergistically facilitated the recombination of relatively useless electrons and holes in hybrid when the interface was irradiated by simulated solar light.Therefore,the remaining electrons and holes with higher reducibility and oxidizability endowed the composite with supreme redox ability.These results were adequately verified by radical trapping experiments,ESR tests,and in situ XPS analyses,suggesting that the electron immigration in the photocatalyst followed the S-scheme heterojunction mechanism.This work can enrich our knowledge of the design and fabrication of novel S-scheme heterojunction photocatalysts and provide a promising strategy for solving environmental pollution in the future.

Integrating non-precious-metal cocatalyst Ni_3N with g-C_3N_4 for enhanced photocatalytic H_2 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^305.4μmol 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%atλ=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.

Solar energy conversion on g-C3N4 photocatalyst:Light harvesting,charge separation,and surface kinetics

Photocatalysis. which utilizes solar energy to trigger chemical reactions, is one of the most desirable solar-energy-conversion approaches. Graphitic carbon nitride （g-C3N4）. as an attractive metal-free photocatalyst, has drawn worldwide research interest in the area of solar energy conversion due to its easy synthesis, earth-abundant nature, physicochemical stability and visible-light-responsive properties. Over the past ten years, g-C3N4 based photocatalysts have experienced intensive exploration, and great progress has been achieved. However, the solar conversion efficiency is still far from industrial applications due to the wide bandgap, severe charge recombination, and lack of surface active sites. Many strategies have been proposed to enhance the light absorption, reduce the recombination of charge carriers and accelerate the surface kinetics. This work makes a crucial review about the main contributions of various strategies to the light harvesting, charge separation and surface kinetics of g-C3N4 photocatalyst. Furthermore, the evaluation measurements for the enhanced light harvesting, reduced charge recombination and accelerated surface kinetics will be discussed. In addition, this review proposes future trends to enhance the photocatalytic performance of g-C3N4 photocatalyst for the solar energy conversion.

Sulfur-mediated photodeposition synthesis of NiS cocatalyst for boosting H2-evolution performance of g-C3N4 photocatalyst

Modification of nickel sulfide cocatalysts is considered to be a promising approach for efficient enhancement of the photocatalytic hydrogen production performance of g-C3N4.Providing more NiS cocatalyst to function as active sites of g-C3N4 is still highly desirable.To realize this goal,in this work,a facile sulfur-mediated photodeposition approach was developed.Specifically,photogenerated electrons excited by visible light reduce the S molecules absorbed on g-C3N4 surface to S^2‒,and subsequently NiS cocatalyst is formed in situ on the g-C3N4 surface by a combination of Ni2+and S2‒due to their small solubility product constant(Ksp=3.2×10^‒19).This approach has several advantages.The NiS cocatalyst is clearly in situ deposited on the photogenerated electron transfer sites of g-C3N4,and thus provides more active sites for H2 production.In addition,this method utilizes solar energy with mild reaction conditions at room temperature.Consequently,the synthesized NiS/g-C3N4 photocatalyst achieves excellent hydrogen generation performance with the performance of the optimal sample(244μmol h^‒1 g^‒1)close to that of 1 wt%Pt/g-C3N4(316μmol h^‒1 g^‒1,a well-known excellent photocatalyst).More importantly,the present sulfur-mediated photodeposition route is versatile and facile and can be used to deposit various metal sulfides such as CoSx,CuSx and AgSx on the g-C3N4 surface,and all the resulting metal sulfide-modified g-C3N4 photocatalysts exhibit improved H2-production performance.Our study offers a novel insight for the synthesis of high-efficiency photocatalysts.

Direct electrospinning method for the construction of Z-scheme TiO_2/g-C_3N_4/RGO ternary heterojunction photocatalysts with remarkably ameliorated photocatalytic performance

A series of Z-scheme TiO2/g-C3N4/RGO ternary heterojunction photocatalysts are successfully constructed via a direct electrospinning technique coupled with an annealing process for the first time. They are investigated comprehensively in terms of crystal structure, morphology, composition, specific surface area, photoelectrochemical properties, photodegradation performance, etc. Compared with binary TiO2/g-C3N4 and single-component photocatalysts, ternary heterojunction photocatalysts show the best photodegradation performance for RhB under stimulated sunlight. This can be attributed to the enlarged specific surface area (111.41 m2/g), the formation of Z-scheme heterojunction, and the high separation migration efficiency of photoexcited charge carriers. A potential Z-scheme mechanism for ternary heterojunction photocatalysts is proposed to elucidate the remarkably ameliorated photocatalytic performance based on active species trapping experiments, PL detection test of hydroxyl radicals, and photoelectrochemical properties.

Enhanced photocatalytic H_2 production over dual-cocatalyst-modified g-C_3N_4 heterojunctions

Ag nanoparticles (NPs) were deposited on the surface of g-C3N4 (CN) by an in situ calcination method. NiS was successfully loaded onto the composites by a hydrothermal method. The results showed that the 10 wt%-NiS/1.0 wt%-Ag/CN composite exhibits excellent photocatalytic H2 generation performance under solar-light irradiation. An H2 production rate of 9.728 mmol·g^-1·h^-1 was achieved, which is 10.82-, 3.45-, and 2.77-times higher than those of pure g-C3N4, 10 wt%-NiS/CN, and 1.0 wt%-Ag/CN composites, respectively. This enhanced photocatalytic H2 generation can be ascribed to the co-decoration of Ag and NiS on the surface of g-C3N4, which efficiently improves light harvesting capacity, photogenerated charge carrier separation, and photocatalytic H2 production kinetics. Thus, this study demonstrates an effective strategy for constructing excellent g-C3N4-related composite photocatalysts for H2 production by using different co-catalysts.

S-scheme Sb2WO6/g-C3N4 photocatalysts with enhanced visible-light-induced photocatalytic NO oxidation performance

Normal photocatalysts cannot effectively remove low-concentration NO because of the high recombination rate of the photogenerated carriers.To overcome this problem,S-scheme composites have been developed to fabricate photocatalysts.Herein,a novel S-scheme Sb2WO6/g-C3N4 nanocomposite was fabricated by an ultrasound-assisted method,which exhibited excellent performance for photocatalytic ppb-level NO removal.Compared with the pure constituents of the nanocomposite,the as-prepared 15%-Sb2WO6/g-C3N4 photocatalyst could remove more than 68%continuous-flowing NO(initial concentration:400 ppb)under visible-light irradiation in 30 min.The findings of the trapping experiments confirmed that•O2^–and h+were the important active species in the NO oxidation reaction.Meanwhile,the transient photocurrent response and PL spectroscopy analyses proved that the unique S-scheme structure of the samples could enhance the charge separation efficiency.In situ DRIFTS revealed that the photocatalytic reaction pathway of NO removal over the Sb2WO6/g-C3N4 nanocomposite occurred via an oxygen-induced route.The present work proposes a new concept for fabricating efficient photocatalysts for photocatalytic ppb-level NO oxidation and provides deeper insights into the mechanism of photocatalytic NO oxidation.

Enhanced photocatalytic activity of TiO_2 nanoparticles using WS_2/g-C_3N_4 hybrid as co-catalyst

TiO2/WS2/g-C3N4composite photocatalysts were synthesized by a liquid-exfoliation-solvothermal method.In this process,the WS2/g-C3N4nano-sheets were prepared by liquid-exfoliation method from the bulk WS2and C3N4in the alcohol system,and then the TiO2nanoparticles(NPs)grew on the WS2/g-C3N4nano-sheets by in-situ synthesized technique.The photocatalytic activity of the as-prepared samples was evaluated by photocatalytic degradation of methyl orange(MO).The results showed that the as-prepared samples exhibited higher photocatalytic activities as compared to the pure TiO2,g-C3N4and TiO2/g-C3N4composite.The enhanced photocatalytic activities of TiO2/WS2/g-C3N4photocatalysts could be attributed to the synergistic effect of heterostructure between TiO2NPs and WS2/g-C3N4nano-sheets,which could efficiently improve the separation of photogenerated electron/hole pairs and utilization efficiency of photons.The quenching tests of radicals indicated that?O2?had crucial effect on degradation of MO,which demonstrated that?O2?was the main active radical in photocatalytic reaction process.

Novel PtPd alloy nanoparticle-decorated g-C_3N_4 nanosheets with enhanced photocatalytic activity for H_2 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.

MgO and Au nanoparticle Co-modified g-C_(3)N_(4)photocatalysts for enhanced photoreduction of CO_(2)with H_(2)O

The photoreduction of CO_(2)to achieve high-value-added hydrocarbons under simulated sunlight irradiation is advantageous,but challenging.In this study,a series of MgO and Au nanoparticle-co-modified g-C_(3)N_(4)photocatalysts were synthesized and subsequently applied for the photocatalytic reduction of CO_(2)with H2O under simulated solar irradiation.The best photocatalytic performance was demonstrated by the Au and 3%MgO-co-modified g-C_(3)N_(4)photocatalysts with CO,CH_(4),CH3OH,and CH3CHO yields of 423.9,83.2,47.2,and 130.4μmol/g,respectively,in a 3-h reaction.We investigated the effects of MgO and Au as cocatalysts on photocatalytic behaviors,respectively.The characterizations and experimental results showed that the enhanced photocatalytic activity was due to the synergistic effect among the components of the ternary photocatalyst.The cocatalyst MgO can activate CO_(2)(adsorbed at the interface between the MgO and Au particles),and the Mg-N bonds formed in the MgO-CN nanosheets played an important role in the charge transfer.Meanwhile,the Au particles that were modified into MgO/g-C_(3)N_(4)can increase the absorption of visible light via the surface plasmon resonance effect and further reduce the activation energies of the photoreduction of CO_(2)using H2O.This study provided an effective method for the modification of traditional primary photocatalysts with promising performance for photocatalytic CO_(2)reduction.

A facile sulfur-assisted method to synthesize porous alveolate Fe/g-C3N4 catalysts with ultra-small cluster and atomically dispersed Fe sites

Heterogeneous catalysts with ultra-small clusters and atomically dispersed(USCAD)active sites have gained increasing attention in recent years.However,developing USCAD catalysts with high-density metal sites anchored in porous nanomaterials is still challenging.Here,through the template-free S-assisted pyrolysis of low-cost Fe-salts with melamine(MA),porous alveolate Fe/g-C3N4 catalysts with high-density(Fe loading up to 17.7 wt%)and increased USCAD Fe sites were synthesized.The presence of a certain amount of S species in the Fe-salts/MA system plays an important role in the formation of USCAD S-Fe-salt/CN catalysts;the S species act as a"sacrificial carrier"to increase the dispersion of Fe species through Fe-S coordination and generate porous alveolate structure by escaping in the form of SO2 during pyrolysis.The S-Fe-salt/CN catalysts exhibit greatly promoted activity and reusability for degrading various organic pollutants in advanced oxidation processes compared to the corresponding Fe-salt/CN catalysts,due to the promoted accessibility of USCAD Fe sites by the porous alveolate structure.This S-assisted method exhibits good feasibility in a large variety of S species(thiourea,S powder,and NH4SCN)and Fe salts,providing a new avenue for the low-cost and large-scale synthesis of high-density USCAD metal/g-C3N4 catalysts.

Synergistic effect of Co（Ⅱ）-hole and Pt-electron cocatalysts for enhanced photocatalytic hydrogen evolution performance of P-doped g-C3N4

g-C3N4 is a metal-free semiconductor and a potential candidate for photocatalytic H2 production,however,the drawbacks,rapid recombination rate and limited migration efficiency of photogenerated carriers,restrict its photocatalytic activity.Herein,Co(II)as a hole cocatalyst modified P-doped g-C3N4 were successfully prepared to ameliorate the separation efficiency of photoinduced carriers and enhance the photocatalytic hydrogen production.The photocatalytic results demonstrated that the P-doped g-C3N4(PCN)exhibited higher photocatalytic activity compared with pure g-C3N4,while Co(II)/PCN photocatalyst exhibited further enhancement of photocatalytic performance.The proposed possible mechanism based on various characterizations is that P-doping can modulate the electronic structure of g-C3N4 to boost the separation of photogenerated-e-and h+;while the synergistic effect of both Co(II)(as hole cocatalyst)and Pt(as electron cocatalyst)can not only lead to the directional shunting of photogenerated e+-h?pairs,but further accelerate the photogenerated electrons transfer to Pt in order to join the photocatalytic reduction process for hydrogen evolution.As a result,the transportation and separation of photoinduced carriers were accelerated to greatest extent in the Pt/Co(II)/PCN photocatalyst.

Preparation and Properties of CdS/Spherical g-C3N4 n-n Heterojunction as a Visible-Light-Driven Photocatalyst for Tetracycline Degradation

The CdS/spherical g-C3N4 n-n heterojunction photocatalyst was fabricated via a solvothermal method.The tetracycline was used to characterize the photocatalytic properties of the as-developed hybrids.The photocatalytic degradation mechanism of the as-developed heterojunction photocatalyst was also analyzed.Research results show that CdS nanoparticles are well dispersed in the surface layer of spherical g-C3N4.Moreover,the mass ratio of CdS to spherical g-C3N4 will influence the photocatalytic activity of the asdeveloped composites,which shows the trend of first increasing and then decreasing as it increased.When the mass ratio is 7:1,in 25 min,the as-developed heterojunction shows 93.2%of the maximum photocatalytic efficiency and still exhibits 83.6%after 5 times cycle testing.Moreover,the as-developed hybrids can accelerate the electron transport and improve the separation efficiency of photo-generated carriers compared with pure samples.In addition,the holes and superoxide radicals are dominating active species during the photocatalytic degradation process.

新型纳米催化剂Pd/g-C_3N_4 NSs的制备及其在Suzuki-Miyaura反应中的应用

通过一步法将纳米Pd负载于二维氮化碳纳米片(g-C3N4)上,制得一种新型的二维纳米催化剂Pd/g-C_3N_4NSs(1),其结构和形貌经TEM,XRD和XPS表征。以卤代苯与取代苯硼酸的Suzuki-Miyaura反应为探针反应,研究了1的催化性能。结果表明:1催化活性较好,TOF为53 000 h-1,部分产物收率高于99%,循环使用3次,其催化性能基本不变。

Facile Fabrication of Fe2O3/Nitrogen Deficient g-C3N4-x Composite Catalysts with Enhanced Photocatalytic Performances

The modification of graphitic carbon nitride can significantly improve the photocatalytic performance of graphitic carbon nitride(g-C3N4).Fe2O3/nitrogen-deficient g-C3N4-x composite catalysts were prepared with dicyandiamide as the precursor and Fe3+doped in this study.The composite catalysts were characterized by XRD,SEM,FT-IR,XPS and photocurrent measurements.Close interaction occurred between Fe2O3 and nitrogen deficient g-C3N4-x,more photogenerated electrons were created and effectively separated from the holes,resulting in a decrease of photocarrier recombination,and thus enhancing the photocurrent.Photocatalytic performance experiments showed that Fe2O3/nitrogen deficient g-C3N4-x could utilize lowenergy visible light more efficiently than pure g-C3N4,and the removal rate was 92%in 60 minutes.