Controlled synthesis of graphitic carbon nitride/beta bismuth oxide composite and its high visible-light photocatalytic activity

g-C₃N₄/β-Bi₂O₃ composites with high visible-light-driven photocatalytic activity were prepared through calcination of g-C₃N₄/Bi₂O₂CO₃ of different proportions. They were characterized by powder X-ray diffraction (XRD), Fourier Translation infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FESEM), transmission electron microscopy TEM (high resolution transmission electron microscopy HRTEM), UV–vis diffuse reflectance spectra (UV–vis DRS) and photoluminescence spectra (PL) techniques. It was observed that the phase structure of Bi₂O₃ is subject to the amount of g-C₃N₄ in the g-C₃N₄/Bi₂O₂CO₃ precursor. Based on the results of light absorption and photocurrent measurement as well as the energy levels of β-Bi₂O₃ and g-C₃N₄, we propose a mechanism for the degradation of organic compounds over this class of catalysts.     

煤基碳量子点/氮化碳复合材料制备及其光催化还原CO2性能

以太西无烟煤为原料,采用化学氧化法制备煤基碳量子点(C-CQDs),进一步以C-CQDs和尿素为前体,原位复合制备得到煤基碳量子点/氮化碳(C-CQDs/g-C₃N₄)复合材料。采用TEM、XRD、FT-IR、UV-Vis、PL等手段对样品结构性能进行了表征和分析,进而考察了其在光催化还原CO₂合成甲醇过程的催化性能。研究表明：C-CQDs均匀地负载在g-C₃N₄的表面,且掺杂适量的C-CQDs有利于提高C-CQDs/g-C₃N₄的光催化活性,当可见光照12 h时,其光催化还原CO₂甲醇产量最高可达28.69 μmol/(g cat),约为相同条件下纯石墨相g-C₃N₄作用时甲醇产量的2.2倍。     

Pomelo biochar as an electron acceptor to modify graphitic carbon nitride for boosting visible-light-driven photocatalytic degradation of tetracycline

In this study, biochar (BC) derived from pomelo was prepared via a high-temperature calcination method to modify the graphitic carbon nitride (g-C₃N₄) to synthesize the BC/g-C₃N₄ composite for the degradation of the tetracycline (TC) antibiotic under visible light irradiation. The experimental results exhibit that the optimal feeding weight ratio of biochar/urea is 0.03:1 in BC/g-C₃N₄ composite could show the best photocatalytic activity with the degradation rate of tetracycline is 83% in 100?min irradiation. The improvement of photocatalytic activity is mainly attributed to the following two points: (i) the strong bonding with π-π stacking between BC and g-C₃N₄ make the photogenerated electrons of light-excited g-C₃N₄ transfer to BC, quickly and improve the separation efficiency of carriers; (ii) the introduction of BC reduces the distance for photogenerated electrons to migrate to the surface and increases the specific surface area for providing more active sites. This study provides a sustainable, economical and promising method for the synthesis of photocatalytic materials their application to wastewater treatment.     

Two-dimensional/two-dimensional Z-scheme photocatalyst of graphitic carbon nitride/bismuth vanadate for visible-light-driven photocatalytic synthesis of imines

As an environmentally friendly strategy, photocatalytic synthesis of imines via selective oxidation of amines has inspired numerous interests. In comparison to conventional type-II heterojunction, the photogenerated electrons and holes on a Z-scheme photocatalyst has strong redox ability. Herein, we prepared a two-dimensional/two-dimensional (2D/2D) Z-scheme photocatalyst of graphitic carbon nitride nanosheet/bismuth vanadate (CNNS/BVO) with a large two-phase interface, which is favorable for the transfer and separation of photoexcited charge carriers. For selective oxidation of benzylamine to N-benzylidenebenzylamine under oxygen atmosphere and visible light irradiation, the CNNS/BVO showed much higher activity than the single CNNS and BVO. The optimized nanocomposite photocatalyst with a 50% CNNS/BVO mass ratio presented a high conversion (~96%) and selectivity (~99%) in 6 h oxidative coupling reaction of benzylamine. More importantly, this 2D/2D CNNS/BVO photocatalyst has good cycling stability, as well as universality for different benzylamine derivatives. Based on the experimental results, a Z-scheme mechanism was determined, where photoinduced electrons were accumulated on the conduction band (CB) of CNNS that is higher than that of BVO and holes were collected on the valence band (VB) of BVO that is lower than that of CNNS. Further, superoxide radicals and photogenerated holes are examined to the mainly active species for selective oxidation of benzylamine, and a possible reaction pathway was therefore proposed. This study demonstrates that the Z-scheme 2D/2D CNNS/BVO with high redox ability is an efficient photocatalyst for the imine synthesis.     

Ag@AgCl quantum dots embedded on Sn3O4 nanosheets towards synergistic 3D flower-like heterostructured microspheres for efficient visible-light photocatalysis

Taking advantage of the oil-water interface, we introduced Ag@AgCl quantum dots (QDs) onto 2D Sn₃O₄ nanosheets to fabricate a composite photocatalyst with a 3D flower-like structure (denoted as Ag@AgCl/Sn₃O₄). Using the degradation of tetracycline hydrochloride (TC-HCl) and methylene blue (MB) as the examples, the as-prepared Ag@AgCl/Sn₃O₄ composite with Ag@AgCl weight loading of 1% indicated 9.6 and 7.88 times higher photocatalytic activity than the Sn₃O₄ nanosheets. Within both degradation reactions, hydroxyl radicals (•OH) and superoxide radicals (•O²⁻) were identified as the critical oxidation intermediates based on radical trapping and electron spin resonance (ESR) experiments. The unique morphology and photoelectrochemical properties of the as-prepared composites suggested the introduced Ag@AgCl QDs cooperated with the Sn₃O₄ semiconductor to enhance the utilization of solar energy. Overall, the established heterojunction helped to reduce the transfer barrier of the photoinduced charge carriers, wherein the surface plasmonic resonance (SPR) of Ag nanoparticles was believed to take the main responsibility. The present work combines the Ag@AgCl-QDs and flower-like 3D Sn₃O₄ microspheres for the first time to achieve an impressive degrading rate of TC-HCl and MB at the Ag@AgCl weight loading as low as 1%.     

Graphene quantum dots prepared from chemical exfoliation of multiwall carbon nanotubes: An efficient photocatalyst promoter

We report here a facile preparation of graphene quantum dots (GQDs) by chemical exfoliation of multiwall carbon nanotubes (MWCNTs) using a modified hummers' method. The resultant GQD samples possess strong electronic property, revealing great potential for photocatalyst design. As an efficient promoter, GQDs/P25 nanocomposites have been successfully prepared by simple wet impregnation and subsequent thermal annealing at 200 °C. In the tests of photocatalytic degradation of organic dyes under visible-light irradiation, the GQDs promoted P25 samples which shows much higher photocatalytic activity compared to the pure P25, indicating the crucial roles of GQDs.     

Explosive thermal exfoliation of intercalated graphitic carbon nitride for enhanced photocatalytic degradation properties

Dicyandiamide derived graphitic carbon nitride (g-C₃N₄) was chemically intercalated by concentrated H₂SO₄ firstly, followed by a rapid heating treatment. Molecules between the stacking layers of g-C₃N₄ produced an explosive effect upon rapid heating to thermally exfoliate g-C₃N₄ into porous structures. The appearance color of g-C₃N₄ changed from light yellow to grey after heating treatment indicating the enhanced light absorption properties, which were identified by the UV–vis absorption test. In addition, photoluminescence intensities of porous g-C₃N₄ were obviously suppressed compared to those of bulk g-C₃N₄ samples, indicating the prevention of the recombination process of photogenerated electron-hole pairs. As a result of these simultaneous modifications in texture, optical and electronic properties, the photodegradation kinetics of crystal violet on the catalyst surface can be improved by 4.75 times.     

Sol-gel synthesis of new TiO2/activated carbon photocatalyst and its application for degradation of tetracycline

A new efficient photocatalyst consisting of TiO₂-activated carbon composite (TiO₂/AC) was synthesized by sol-gel process and applied to decomposition of tetracycline (TC). Its properties and catalytic activity were evaluated in comparison with bare TiO₂ and P25, based on several characterization techniques and TC photodegradation kinetic studies. The results showed TiO₂/AC has better structural and electronic features for photocatalysis; S_BET of 129 m² g^–1, exclusively anatase phase, crystal size of 8.53 nm and band gap energy of 3.04 eV. The catalytic activity of the material was evaluated based on photodegradation kinetic studies of TC from aqueous solution (with initial concentration=50 mg L⁻¹ and catalyst dosage=1.0 g L⁻¹). Non-linear kinetic model of pseudo-first order were fitted to the resulting experimental data. The apparent first-order rate constant (k_app=42.9×10^–3 min^–1) and half-life time (t_1/2=16.1 min) determined for TiO₂/AC were better than those for P25 and bare TiO₂. TC degradation by-products were investigated by HPLC-MS, showing TC was completely degraded after 75 min, producing fragments with m/z smaller than 150.     

Superior adsorption performance of graphitic carbon nitride nanosheets for both cationic and anionic heavy metals from wastewater

Water pollution caused by highly toxic Cd(II), Pb(II), and Cr(VI) is a serious problem. In the present work,a green and low-cost adsorbent of g-C_3N_4 nanosheets was developed with superior capacity for both cationic and anionic heavy metals. The adsorbent was easily fabricated through one-step calcination of guanidine hydrochloride with thickness less than 1.6 nm and specific surface area of 111.2 m~2·g~(-1). Kinetic and isotherm studies suggest that the adsorption is an endothermic chemisorption process, occurring on the energetically heterogeneous surface based on a hybrid mechanism of multilayer and monolayer adsorption. The tri-s-triazine units and surface N-containing groups of g-C_3N_4 nanosheets are proposed to be responsible for the adsorption process.Further study on pH demonstrates that electrostatic interaction plays an important role. The maximum adsorption capacity of Cd(II), Pb(II), and Cr(VI) on g-C_3N_4 nanosheets is 123.205 mg·g~(-1), 136.571 mg·g~(-1),and 684.451 mg·g~(-1), respectively. The better adsorption performance of the adsorbent than that of the recently reported nanomaterials and low-cost adsorbents proves its great application potential in the removal of heavy metal contaminants from wastewater. The present paper developed a promising adsorbent which will certainly find applications in wastewater treatment and also provides guiding significance in designing adsorption processes.     

Ultrathin graphitic carbon nitride nanosheets and graphene composite material as high-performance PtRu catalyst support for methanol electro-oxidation

Graphitic carbon nitride (g-C₃N₄) has been demonstrated as an advanced support material for Pt nanoparticles (NPs) due to its excellent stability and abundant Lewis acid for anchoring metal NPs. However, its non-conductive nature and low surface areas still impede its application in electrochemical fields. Herein, a π–π stacking method is presented to prepare graphene/ultrathin g-C₃N₄ nanosheets composite support for PtRu catalyst. The weaknesses of g-C₃N₄ are greatly overcome by establishing a 2D layered structure. The significantly enhanced performance for this novel PtRu catalyst is ascribed to reasons as follows: the homogeneous dispersion of PtRu NPs on g-C₃N₄ nanosheets due to its abundant Lewis acid sites for anchoring PtRu NPs; the excellent mechanical resistance and stability of g-C₃N₄ nanosheets in acidic and oxidative environments; the increased electron conductivity of support by forming a layered structure and the strong metal-support interaction (SMSI) between metal NPs and g-C₃N₄ NS.     

Porous graphitic carbon nitride synthesized via direct polymerization of urea for efficient sunlight-driven photocatalytic hydrogen production

Energy captured directly from sunlight provides an attractive approach towards fulfilling the need for green energy resources on the terawatt scale with minimal environmental impact. Collecting and storing solar energy into fuel through photocatalyzed water splitting to generate hydrogen in a cost-effective way is desirable. To achieve this goal, low cost and environmentally benign urea was used to synthesize the metal-free photocatalyst graphitic carbon nitride (g-C(3)N(4)). A porous structure is achieved via one-step polymerization of the single precursor. The porous structure with increased BET surface area and pore volume shows a much higher hydrogen production rate under simulated sunlight irradiation than thiourea-derived and dicyanamide-derived g-C(3)N(4). The presence of an oxygen atom is presumed to play a key role in adjusting the textural properties. Further improvement of the photocatalytic function can be expected with after-treatment due to its rich chemistry in functionalization.     

Preparation of molecularly imprinted fluorescence sensor based on carbon quantum dots via precipitation polymerization for fluorescence detection of tetracycline

A facile and effective method was proposed to prepare the molecularly imprinted fluorescence sensor with carbon quantum dots, which were modified vinyl groups by acrylic acid on the surface. The obtained fluorescence composite material was investigated by transmission electron microscope and Fourier transform infrared spectra. After the experimental conditions were optimized, a linear range of 1.0–60 μmol L⁻¹ was obtained and the detection limit was 0.17 μmol L⁻¹. The novel fluorescence sensor can be successfully used to detect tetracycline in real samples. This study provides a convenient strategy for selective recognition and rapid detection of tetracycline in the complex environment.     

PMoA/CS/P25纳米复合光催化剂的制备及光催化降解盐酸四环素

通过水热和浸渍相结合的方法将壳聚糖(CS)、P25、磷钼酸(PMoA)三者结合起来,制备了PMoA/CS/P25纳米复合光催化剂,研究其对不同浓度盐酸四环素的降解效果,考察了不同PMoA负载量对其光催化效果的影响。结果表明,当PMoA的负载量为0.08 g,盐酸四环素的浓度为20 mg/L时的光催化效果最好。     

Facile assembly of TiO2 nanospheres/SnO2 quantum dots composites with excellent photocatalyst activity for the degradation of methyl orange

In this report, SnO₂ quantum dots anchored on TiO₂ nanospheres (TiO₂/SnO₂ composites) have been synthesized by a simple one-step hydrothermal process, and then employed as photocatalyst in photodegradation system. The microstructure of TiO₂/SnO₂ composites reveals that the SnO₂ quantum dots are dispersed on the surface of TiO₂ nanospheres uniformly. The photocatalytic behavior of the as-prepared samples revealed that the composites exhibited highly efficient performance by degrading 100 mL of 10 mg/L methylene orange in 15 min completely under ultraviolet-visible light. Owning to the special structure of the composites, TiO₂/SnO₂ shows a more UV–vis light absorption than either pure TiO₂ nanospheres or pure SnO₂ quantum dots. This study offers a facile method to prepare TiO₂/SnO₂ composites, which will be a choice for greatly extending potential applications in water pollution treatment, degradation of pollutants and other related fields.     

Construction of CaTiO3 nanosheets with boron nitride quantum dots as effective photogenerated hole extractor for boosting photocatalytic performance under simulated sunlight

Herein, titanate-based perovskite CaTiO₃ nanosheets were successfully designed via boron nitride quantum dots (BNQDs) to fabricate CaTiO₃/BNQDs catalyst. The as-fabricated composite catalysts were analysed by transmission electron microscope (TEM), scanning electron microscopy coupled with energy dispersive spectrometry (SEM-EDS), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR), X-ray diffraction (XRD), UV–vis spectroscopy (UV-DRS), photoluminescence (PL) and electrochemical impedance spectroscopy (EIS) techniques. SEM-Mapping analysis showed that the boron and nitrogen elements dispersed well over the CaTiO₃ surface which was useful for building electronic channels for rapid transport of photo-induced charge pairs. TEM images verified the attachment of BNQDs around the surface of host CaTiO₃ forming intimate interface while the distribution of chemical states was observed by XPS analysis demonstrating strong coupling effect between BNQDs and CaTiO₃ through Ti–O–N and Ti–O–B bonds. Moreover, PL and light absorption properties enhanced with the quantum confinement effect of BNQDs. As expected, the photocatalytic degradation rate of CaTiO₃/BNQDs was increased to k_app = 0.015 min^{? 1} with optimum BNQDs loading, which was 2.31 times folder than that of bare CaTiO₃ (0.006 min^{? 1}). The enhanced photocatalytic efficiency was observed for CaTiO₃/BNQDs than pristine perovskite on account of formation of electron tapping sites, decreased band gap energy and hindered recombination rate. On the other hand, in the presence of H₂O₂, the degradation percentage increased from 88.5% to 92.1% at the end of 120 min of irradiation while 96.8% of TC was quickly degraded within 60 min after activating with peroxymonosulfate which created strong sulphate radicals. Radical trapping tests indicated that the photo-generated holes were the primary active species in the photocatalytic mechanism. Moreover, CaTiO₃/BNQDs catalyst showed excellent stability in recycling tests. Besides, the possible degradation mechanism was proposed. This study shed light on the significance of BNQDs in the enhancement of the photocatalytic activities of titanate-based perovskite for effective degradation of tetracycline antibiotic in contaminated water.     

Bio-inspired ZnS quantum dots as efficient photo catalysts for the degradation of methylene blue in aqueous phase

ZnS quantum dots are semiconductor nanoparticles characterized by superior optoelectronic properties. The amenability of these nanoparticles in initiating efficient photo-redox reactions enable their use as photocatalysts for environmental remediation. In the present study, ZnS quantum dots were biosynthesized from Zn tolerant Penicillium sp. under ambient reaction conditions. The biogenic ZnS quantum dots were characterized using TEM, SEM, XRD, FTIR and UV–Vis absorption studies that revealed the formation of spherical particles of average diameter 11.08?nm with a zinc blend crystal structure and the optical properties were in par with chemically synthesized ZnS. The biogenic ZnS were then used for the photodegradation of methylene blue (MB) dye. It was found that the green synthesized ZnS quantum dots exhibited good photocatalytic activity with a half-life of 4?h. Further, the dye degradation efficiency was enhanced as the ZnS nanocatalyst/dye ratio increased and reached equilibrium within 6?h. The present study reports an inexpensive and scalable method to fabricate ZnS nano hybrids with practical applicability in the remediation of pollutants in textile, paper and dyeing industry.     

Synthesis and characterization of polypyrrole/graphitic carbon nitride/niobium pentoxide nanocomposite for high-performance energy storage applications

Graphitic carbon nitride (GCN) has been employed as a supercapacitor electrode because of its high carbon-to-nitrogen ratio and flexible structure. However, its low surface area and poor conductivity continue to be obstacles for practical usage. GCN's electrochemical characteristics are enhanced by the hybrid structure it forms with polypyrrole and Nb₂O₅. The synthesized polypyrrole (Ppy)/GCN/niobium pentoxide (Nb₂O₅) (Ppy/GCN/Nb₂O₅) nanocomposite electrode was tested for supercapacitance by cyclic voltammetry (CV) and Alternating current impedance techniques in 6 M Potassium hydroxide(KOH) electrolyte. The Ppy/GCN/Nb₂O₅ is linked to a network of agglomerated GCN and Nb₂O₅ nanoparticles with additional spherical shapes. The specific capacitance of Ppy/GCN/Nb₂O₅ was determined to be 1177 Fg⁻¹ at a current density of 5 Ag⁻¹. The Ppy/GCN/Nb₂O₅ electrode in KOH has average specific energy and specific power densities of 33 Wh kg⁻¹ and 2991 W kg⁻¹, respectively. The electrode showed excellent capacitance-retention ability of 97% after 10,000 cycles. The results demonstrate the high stability and efficient performance of the Ppy/GCN/Nb₂O₅ electrode employed in supercapacitors. The performance of the Ppy/GCN/Nb₂O₅ electrode was found to be superior to those reported for other carbon-based materials.     

ZIF-8负载海藻酸钠/氧化石墨烯基底用于吸附盐酸四环素

为了解决金属-有机骨架材料ZIF-8在水溶液中难以回收的问题，以海藻酸钠（SA）为基础材料，采用直接滴加法将SA和氧化石墨烯（GO）混合溶胶滴入Ca2+溶液中，交联形成SA/GO凝胶基底，再将ZIF-8原位生长在SA/GO基底上，制得SA/GO/ZIF-8复合吸附剂用于去除环境废水中盐酸四环素（TC）。XRD、TEM和SEM表征结果证明ZIF-8在SA/GO凝胶基底上均匀生长，且经计算得ZIF-8的负载率高达34.21%。当温度为25 ℃、pH=7及TC浓度为50 mg/L时，30 mg SA/GO/ZIF-8复合吸附剂对TC的平衡吸附容量可达125.37 mg/g。吸附动力学和等温线结果表明SA/GO/ZIF-8对TC的吸附过程受化学活性位点控制，属于活性位点均匀的单层吸附。在循环吸附6次后，SA/GO/ZIF-8复合吸附剂对TC的去除率仍在85%以上。这种易于分离和高负载ZIFs的SA/GO/ZIF-8复合吸附剂有望成为去除废水中抗生素的理想选择。