Z-scheme TiO2/g-C3N4 composites prepared by hydrothermal assisted thermal polymerization with enhanced visible light photocatalytic activity

Melamine was added to the precursor of TiO₂, then TiO₂ prepared by hydrothermal, while melamine was modified. Subsequently, a series of Z-scheme TiO₂/g-C₃N₄ heterojunction composites were successfully synthesized by simple calcination. The morphology and structure of samples were characterized by XRD, FT-IR, UV–vis DRS, SEM, TEM, PL and BET. The photocatalytic activity of these samples has been investigated by degradation of Rhodamine B (RhB), and results indicated that photocatalytic activity of the as-prepared samples was greatly influenced by the content of titanium tetrabutoxide in precursors and the hydrothermal time. The degradation rate of TiO₂/g-C₃N₄-1 to RhB was the best, which was 5.05-fold of pure TiO₂ (19.61%) and 2.25-fold of bulk g-C₃N₄ (44.06%), respectively. The trapping experiment results showed that ^·O₂^? and h⁺ were main active species during degradation of RhB. The photocatalytic activity of the sample did not decrease significantly after 4 cycles. The unique Z-scheme heterojunction between TiO₂ and g-C₃N₄ improved photocatalytic activity of the samples under visible light.

     

Facile synthesis of GO as middle carrier modified flower-like BiOBr and C3N4 nanosheets for simultaneous treatment of chromium(VI) and tetracycline

A novel GO modified g-C₃N₄ nanosheets/flower-like BiOBr hybrid photocatalyst is fabricated by a facile method. The characterization results reveal that wrinkled GO is deposited between g-C₃N₄ nanosheets and flower-like BiOBr forming a Z-scheme heterojunction. As a mediator, plicate GO plays a positive role in prompting photogenerated electrons transferring through its sizeable 2D/2D contact surface area. The g-C₃N₄/GO/BiOBr hybrid displays a superior photocatalytic ability to g-C₃N₄ and BiOBr in photodegrading tetracycline (TC), whose removal efficiency could reach 96% within 2 h. Besides, g-C₃N₄/GO/BiOBr composite can reduce Cr(VI), and simultaneously treat TC and Cr(VI) combination contaminant under the visible light. The g-C₃N₄/GO/BiOBr ternary composite also exhibits satisfactory stability and reusability after four cycling experiments. Further, a feasible mechanism related to the photocatalytic process of g-C₃N₄/GO/BiOBr is put forward. This study offers a ternary hybrid photocatalyst with eco-friendliness and hopeful application in water pollution.     

Direct electrospinning method for the construction of Z-scheme TiO2/g-C3N4/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.     

Degradation of tetracycline hydrochloride by ultrafine TiO2 nanoparticles modified g-C3N4 heterojunction photocatalyst: Influencing factors,products and mechanism insight

The unique heterojunction photocatalyst of graphite carbon nitride（g-C₃N₄） modified ultrafine TiO₂（gC₃N₄/Ti O₂） was successfully fabricated by electrochemical etching and co-annealing method. However,the effects of various environmental factors on the degradation of TC by g-C₃N₄/Ti O2and the internal reaction mechanism are still unclear. In this study, the effects of initial p H, anions, and cations on the ph...     

Bi2Fe4O9/g-C3N4/UiO-66三元复合材料的协同光催化作用

通过水热法合成具有协同机制的三元复合材料Bi₂Fe₄O₉/g-C₃N₄/UiO-66,研究表明三元复合光催化剂的催化活性要高于二元材料和纯材料。这主要是由于Bi₂Fe₄O₉更易于和g-C₃N₄结合形成稳定的Z-scheme异质结结构,使三元复合材料增强了可见光响应能力,提高了电子-空穴分离能力,增强了空穴和电子的氧化还原能力。     

Bi2Fe4O9/g-C3N4/UiO-66三元复合材料的协同光催化作用

通过水热法合成具有协同机制的三元复合材料Bi₂Fe₄O₉/g-C₃N₄/UiO-66,研究表明三元复合光催化剂的催化活性要高于二元材料和纯材料。这主要是由于Bi₂Fe₄O₉更易于和g-C₃N₄结合形成稳定的Z-scheme异质结结构,使三元复合材料增强了可见光响应能力,提高了电子-空穴分离能力,增强了空穴和电子的氧化还原能力。     

Interfacial engineering of graphitic carbon nitride (g-C3N4)-based metal sulfide heterojunction photocatalysts for energy conversion: A review

As one of the most appealing and attractive technologies, photocatalysis is widely used as a promising method to circumvent the environmental and energy problems. Due to its chemical stability and unique physicochemical, graphitic carbon nitride (g-C₃N₄) has become research hotspots in the community. However, g-C₃N₄ photocatalyst still suffers from many problems, resulting in unsatisfactory photocatalytic activity such as low specific surface area, high charge recombination and insufficient visible light utilization. Since 2009, g-C₃N₄-based heterostructures have attracted the attention of scientists worldwide for their greatly enhanced photocatalytic performance. Overall, this review summarizes the recent advances of g-C₃N₄-based nanocomposites modified with transition metal sulfide (TMS), including (1) preparation of pristine g-C₃N₄, (2) modification strategies of g-C₃N₄, (3) design principles of TMS-modified g-C₃N₄ heterostructured photocatalysts, and (4) applications in energy conversion. What is more, the characteristics and transfer mechanisms of each classification of the metal sulfide heterojunction system will be critically reviewed, spanning from the following categories: (1) Type I heterojunction, (2) Type II heterojunction, (3) p-n heterojunction, (4) Schottky junction and (5) Z-scheme heterojunction. Apart from that, the application of g-C₃N₄-based heterostructured photocatalysts in H₂ evolution, CO₂ reduction, N₂ fixation and pollutant degradation will also be systematically presented. Last but not least, this review will conclude with invigorating perspectives, limitations and prospects for further advancing g-C₃N₄-based heterostructured photocatalysts toward practical benefits for a sustainable future.     

Z型异质结Au/CoWO4/g-C3N4的制备及其光催化降解性能

采用浸渍-煅烧方法将Au引入到g-C₃N₄纳米片（CNs）与CoWO₄复合材料中得到Z型异质结光催化剂Au/CoWO₄/CNs（Au/ CoNs-x,x=5、10、20、50）。Au作为电荷传输通道加快了光生电子从CoWO₄迁移至CNs的速度。与CoWO₄/CNs相比,Au/CoNs-10展示出优异的光催化降解亚甲基蓝和盐酸四环素活性,其表观速率常数分别从0.289和0.360 h^-1提升至0.499和0.637 h^-1。光电测试与自由基捕获实验表明,Au/CoNs-10光催化性能的显著提升主要是由于Z型异质结的构建降低了光生电子-空穴的复合速率,同时促使具有高氧化活性的羟基自由基（·OH）和超氧自由基（·O₂^-）的形成。     

Flower-like shaped Bi12TiO20/g-C3N4 heterojunction for effective elimination of organic pollutants: Preparation,characterization, and mechanism study

Flower-like shaped Bi₁₂TiO₂₀ (Bismuth Titanate)/g-C₃N₄ (graphite-like carbon nitride) heterojunction was prepared through hydrothermal and sonification methods for the degradation of organic pollutants by visible-light irradiation. The preparation process, chemical structures, and the mechanism of photocatalytic enhancement of the heterostructures were studied systematically. Under visible-light irradiation, the novel flower-like shaped Bi₁₂TiO₂₀/g-C₃N₄ heterojunction demonstrates prominent activities for the degradation of rhodamine B and p-nitrophenol, with the introduction of flower-like shaped Bi₁₂TiO₂₀ into g-C₃N₄ composites greatly increasing the activity of pure g-C₃N₄. This activity enhancement for the heterojunction could be mainly attributed to its low recombination speed of electron–hole pairs, high adsorption ability of organic pollutants, and better optical absorption ability. Moreover, in the visible-light system of Bi₁₂TiO₂₀/g-C₃N₄, ^•OH also contributed to the degradation of pollutants, which may explain the enhanced photocatalytic activity after the introduction of Bi₁₂TiO_20, as ^•OH is inactive in pure g-C₃N₄. Furthermore, 10 wt.% Bi₁₂TiO₂₀/g-C₃N₄ showed not only high activity but also good stability for degradation of aqueous organic pollutants, implying potential applications prospect.     

Two-step calcination synthesis of Z-scheme α-Fe2O3/few-layer g-C3N4 composite with enhanced hydrogen production and photodegradation under visible light

Solar photocatalytic technology is of great significance for adjusting energy structure and environmental improvement. Developing an efficient and low-cost photocatalyst is key to realizing the conversion of solar to chemical energy. In this study, α-Fe₂O₃-modified few-layer g-C₃N₄ hybrids (α-Fe₂O₃/FL g-C₃N₄) were successfully prepared by a two-step calcination route with a mixture of α-Fe₂O₃ and melamine. The samples were characterized by Thermogravimetric analysis, X-ray diffraction, Fourier transform infrared, scanning electron microscope, transmission electron microscope, High-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, Brunauer–Emmett–Teller, UV–Vis absorption spectrum, photoluminescence, and Time-resolved photoluminescence spectroscopy; furthermore, their photoelectrochemical measurements and their photocatalytic performances were evaluated by visible light-driven hydrogen evolution and degradation of RhB. The results showed that the hydrogen production activity and degradation ability of α-Fe₂O₃/FL g-C₃N₄ were significantly enhanced compared with those of α-Fe₂O₃ / multilayer g-C₃N₄ (α-Fe₂O₃/ML g-C₃N₄) and FL g-C₃N₄. The enhanced photoactivities were mainly attributed to the synergistic effect between the increased visible-light absorption, enhanced surface area, and highly efficient electron transfer and separation on the Z-type heterojunction interface. This work not only provides evidence for the formation of FL g-C₃N₄ nanosheets using a thermal exfoliation method but also provides new insights into the interfacial charge carrier dynamics of Z-scheme α-Fe₂O₃/FL g-C₃N₄ heterostructures for photocatalytic H₂ generation and pollutant degradation.     

Construction of direct Z-scheme g-C3N4/TiO2 nanorod composites for promoting photocatalytic activity

Direct Z-scheme g-C₃N₄/TiO₂ nanorod composites were prepared for enhancing photocatalytic activity for pollutant removal. The characterization revealed that the g-C₃N₄/TiO₂ nanorod composite formed a close interface contact between g-C₃N₄ and TiO₂ nanorods, which was of benefit for the charge transfer and resulted in its high photocatalytic activity. The g-C₃N₄/TiO₂ nanorod composites exhibited higher photocatalytic activity for degradation of Rhodamine B (RHB) than bare g-C₃N₄ and TiO₂ nanorods. The high photocatalytic activity of g-C₃N₄/TiO₂ nanorod composites is attributed to the formation of the direct Z-scheme system, in which the electrons from the conduction band (CB) of TiO₂ combine with the holes from the valence band (VB) of C₃N₄ while the electrons from the CB of C₃N₄ and holes from the VB of TiO₂ with stronger redox ability are used to reduce and oxidize pollutants. Based on the radical-trapping experiments, the main reactive species for RHB degradation are O₂⁻ and · OH, which are produced by photoinduced electrons and holes with high redox ability. This work provides insights into the photocatalytic mechanism of composite materials for the photocatalytic removal of organic pollutants.     

中空管状g-C3N4/Ag3PO4复合催化剂的制备及其可见光催化性能

采用化学沉淀法制备中空管状 g-C₃N₄/Ag₃PO₄复合催化剂。通过 X射线衍射(XRD)、扫描电子显微镜(SEM)、紫外可见漫反射光谱(UV-Vis DRS)和荧光光谱对其结构、形貌和光学性能进行了表征。结果表明：Ag₃PO₄纳米颗粒均匀地分散在中空管状g-C₃N₄表面,两者紧密结合形成异质结。研究复合催化剂在可见光照射下降解盐酸四环素(TC)的光催化活性。结果显示：复合催化剂在80 min内对TC的降解率为98%,其降解反应速率常数是纯相Ag₃PO₄的3倍。经过5次循环实验后复合催化剂对于TC的降解率仍保持87%,具有优良的循环稳定性。捕获实验表明空穴(h⁺)和超氧负离子(·O₂^ˉ)是光催化反应过程中的主要活性物种。根据能带理论,提出了复合催化剂异质结的Z型光催化机理。     

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.     

Highly Efficient Ag3PO4/g-C3N4 Z-Scheme Photocatalyst for Its Enhanced Photocatalytic Performance in Degradation of Rhodamine B and Phenol

Ag₃PO₄/g-C₃N₄ heterojunctions, with different g-C₃N₄ dosages, were synthesized using an in situ deposition method, and the photocatalytic performance of g-C₃N₄/Ag₃PO₄ heterojunctions was studied under simulated sunlight conditions. The results revealed that Ag₃PO₄/g-C₃N₄ exhibited excellent photocatalytic degradation activity for rhodamine B (Rh B) and phenol under the same light conditions. When the dosage of g-C₃N₄ was 30%, the degradation rate of Rh B at 9 min and phenol at 30 min was found to be 99.4% and 97.3%, respectively. After five cycles of the degradation experiment for Rh B, g-C₃N₄/Ag₃PO₄ still demonstrated stable photodegradation characteristics. The significant improvement in the photocatalytic activity and stability of g-C₃N₄/Ag₃PO₄ was attributed to the rapid charge separation between g-C₃N₄ and Ag₃PO₄ during the Z-scheme charge transfer and recombination process.     

Synergistic improvement of Cr(VI) reduction and RhB degradation using RP/g-C3N4 photocatalyst under visible light irradiation

The RP/g-C₃N₄ heterojunction photocatalyst was fabricated by a facile heat treatment strategy. The obtained composite has excellent light harvesting ability and charge separation performance. Compared to single RP and g-C₃N₄, the 50%-RP/g-C₃N₄ exhibited enhanced photocatalytic activity for simultaneously removing Cr(VI) and RhB, and the removal rates can reach 92% and 99% in 25 min, respectively. The enhanced mechanism was revealed by active species capturing experiments, showing that electrons can reduce Cr(VI) and produce O₂^– in air and that holes can directly oxidize the dyes. The coexistence of Cr(VI) and RhB will lead to a synergistic improvement of Cr(VI) reduction and RhB degradation due to rapid surface reactions. This further improves the charge separation except for the heterojunction effect. In addition, the COD analysis demonstrates that organic dyes are mainly degraded into CO₂, H₂O and some intermediates.     

碳化MoS2/掺硫g-C3N4异质结的合成及其在可见光下催化降解罗丹明B机理

为了进一步提高聚合物半导体类石墨相氮化碳（g-C₃N₄）降解有机物的活性,通过简单的水热法复合得到碳化MoS₂/掺硫g-C₃N₄异质结（MoSC/S-CN）,并在可见光下研究其罗丹明B （RhB）的降解性能。结果表明,相较于纯g-C₃N₄,最优化的MoSC/S-CN样品对可见光的吸收范围得到明显拓宽,并且在100 min内对RhB的降解效率为92.5%,比纯g-C₃N₄性能提高68.83%。一系列的结构和光学性质表明,掺硫后再进一步与碳化MoS₂耦合可以协同作用于g-C₃N₄,改善g-C₃N₄的能带结构,加速光生电子空穴对的分离,有效提高光催化活性。     

Two-dimensional g-C3N4 nanosheets-based photo-catalysts for typical sustainable processes

Graphitic carbon nitride (g-C₃N₄) has been widely studied as a visible light responsive photocatalyst in recent years, due to its facile synthesis, low cost, high stability, and appropriate bandgap/band positions. In this review, we firstly introduce and compare various exfoliation approaches of bulk g-C₃N₄ into ultrathin g-C₃N₄ nanosheets. Then, many modification strategies of g-C₃N₄ nanosheets are also reviewed, including heterojunction construction, doping, defect control, and structure design. Thereafter, the charge transfer mechanism in g-C₃N₄ nanosheets based heterojunctions is present, e.g., Z-scheme, S-scheme and other forms. Besides, the photocatalytic applications of g-C₃N₄ nanosheets based photocatalysts are summarized including environmental remediation, energy generation and storage, organic synthesis, and disinfection. This review ends with a summary and some perspectives on the challenges and new directions in exploring g-C₃N₄ nanosheets-based photocatalysts.     

BiOBr/g-C3N4 S型异质结无H2O2光-自芬顿高效催化降解RhB

通过焙烧-超声混合法成功地制备了BiOBr/g-C₃N₄ S型异质结复合光催化剂。采用多种表征手段对样品物理属性进行了表征,包括X射线多晶粉末衍射仪(XRD)、扫描电子显微镜(SEM)、X射线光电子能谱(XPS)、紫外可见漫反射光谱(UV-VisDRS)。研究了所制备样品有/无Fe³⁺的光-自芬顿催化/光催化降解罗丹明B (RhB)性能。通过捕获实验确定了光催化反应中的主要活性物种,提出了光-自芬顿反应的降解机理。研究结果表明,BiOBr/g-C₃N₄ S型异质结能原位生成H₂O₂,添加Fe³⁺后,H₂O₂被原位活化成活性物种且光生电流和载流子分离效率获得显著提高。该光-自芬顿过程能高效降解RhB,其反应速率常数为0.208 min^-1,约为无Fe³⁺光催化反应速率常数的5.3倍,在光-自芬顿循环使用过程中表现出良好的稳定性。Fe³⁺的加入促进了光生电荷的分离和H₂O₂的活化,超氧阴离子自由基(·O₂^-)、空穴和羟基是光-自芬顿催化过程中的主要活性物种,且·O₂^-作用更大。     

Efficient Z-scheme g-C3N4/MoO3 heterojunction photocatalysts decorated with carbon quantum dots: improved visible-light absorption and charge separation

Z-scheme heterojunction photocatalysts based on g-C₃N₄ generally need to recombine g-C₃N₄ and a wide bandgap semiconductor. This structure is limited by the large bandgap of the constituent material, which can effectively suppress carrier recombination while limiting the absorption of visible light. Due to the superior up-conversion photoluminescence properties of the carbon quantum dots (CQDs), this dilemma can be solved ingeniously by adding CQDs to the composite. Moreover, the charge reservoirs of CQDs are conducive to the charge carrier separation effect. In this work, a novel CQDs-modified Z-type photocatalyst is constructed and the successful implantation of CQDs is demonstrated. The composite catalyst exhibits broad-spectrum response to visible light and the overall performance is obviously superior to that of the binary MoO₃/g-C₃N₄ heterojunction. The high efficiency and versatility of the degradation imply that the newly prepared CQDs/g-C₃N₄/MoO₃ is a versatile photocatalyst for the removal of various target pollutants in the environment.

     

BiOBr/g-C3N4 S型异质结无H2O2光-自芬顿高效催化降解RhB

通过焙烧-超声混合法成功地制备了BiOBr/g-C₃N₄S型异质结复合光催化剂。采用多种表征手段对样品物理属性进行了表征,包括X射线多晶粉末衍射仪(XRD)、扫描电子显微镜(SEM)、X射线光电子能谱(XPS)、紫外可见漫反射光谱(UV-Vis DRS)。研究了所制备样品有/无Fe³⁺的光-自芬顿催化/光催化降解罗丹明B(RhB)性能。通过捕获实验确定了光催化反应中的主要活性物种,提出了光-自芬顿反应的降解机理。研究结果表明,BiOBr/g-C₃N₄S型异质结能原位生成H₂O₂,添加Fe³⁺后,H₂O₂被原位活化成活性物种且光生电流和载流子分离效率获得显著提高。该光-自芬顿过程能高效降解RhB,其反应速率常数为0.208 min^-1,约为无Fe³⁺光催化反应速率常数的5.3倍,在光-自芬顿循环使用过程中表现出良好的稳定性。Fe...