Significantly enhanced visible-light photocatalytic activity of g-C3N4 via ZnO modification and the mechanism study

Efficient visible-light-active ZnO/Cs0.33WO3/g-C3N4 double Z-type heterojunction photocatalyst for rhodamine B photodegradation

Developing highly efficient photocatalyst systems for the removal of cancer-causing organic dye substances from polluted water and wastewater is now in high demand because of the growing problem of contaminated water. An affordable technique was employed to create a ternary ZnO/Cs0.33WO3/g-C3N4 heterojunction nanocomposite with highly efficient and rapid photodegradation capabilities for degrading rhodamine B (RhB) dye. Using visible-light irradiation, the photocatalytic tests revealed that the proposed ZnO/Cs0.33WO3/g-C3N4 heterojunction nanocomposite is efficiently able to degrade more than 91 % of RhB dye within 15 min, 97.5 % within 20 min, and 99.9 % within 30 min, which is significantly efficient compared to sole ZnO and Cs0.33WO3. The kinetic rate constant of RhB photodegradation catalyzed by the ternary ZnO/Cs0.33WO3/g-C3N4 nanocomposite is assessed to be about 31 times faster than that of Cs0.33WO3 and about 3.5 times faster than that of ZnO. The investigation of the photodegradation mechanism suggested that the ternary ZnO/Cs0.33WO3/g-C3N4 nanocomposite follows a direct Z-scheme mechanism for charge transfer. The creation of a ternary ZnO/Cs0.33WO3/g-C3N4 heterojunction nanocomposite is valuable for increasing the surface area, strengthening the contact between its components, enhancing absorption capacity of visible light, increasing the generation rate of the photoexcited charge carriers, improving the separation efficiency of photogenerated charge carriers, and reducing their undesired recombination rate. As a consequence, the visible-light-mediated degradation of organic dye contaminants is significantly improved.

In situ synthesis of ZnO/g-C3N4 based composites for photodegradation of methylene blue under visible light

In this study, in situ-synthesized ZnO/g-C3N4 based composites were used as photocatalysts for organic pollution removal. These nanocomposites were prepared through simple calcination of a mixture of melamine and ZnO nanoparticles and underwent comprehensive evaluation of their structural, morphological, optical, and photocatalytic properties, using various analytical techniques. As the g-C3N4 content increased, the band gap decreased from 3.02 to 2.94 eV. Additionally, the reduction in photoluminescence intensity confirmed the heterojunction interface between the g-C3N4 and ZnO components. The photodegradation rate of methylene blue (MB) dye exhibited an increase, rising from 0.016 (min-1) for ZnO and 0.011 (min-1) for g-C3N4 to 0.022 (min-1) for the ZnO/g-C3N4 (10 wt%) composite. Furthermore, combining ZnO (50 wt%) with g-C3N4 led to a significant enhancement in the MB dye removal efficiency, reaching 97% compared to the ZnO/g-C3N4 (10 wt%) composite. In contrast, the removal efficiencies were 90% for pristine ZnO and 73% for g-C3N4 phases.

Visible Light Induced Photocatalytic Degradation of Diclofenac in Aqueous Solution Using Fabricated ZnO/g-C3N4 by Facile Calcination Technique

The ability of the heterojunction between two distinct semiconductors with appropriately matched band gaps to improve the separation of photogenerated electron-hole pairs has been demonstrated to enhance photocatalytic activity. Hence, ZnO/g-C3N4 composites have been fabricated by the facile deposition and calcination of ZnO and g-C3N4. X-ray photoelectron spectroscopy, powder X-ray diffraction, and Fourier transform infrared spectroscopy confirm the formation of the composite. Scanning electron microscope, transmission electron microscope, and energy-dispersive X-ray spectroscopy morphological analysis reveal that ZnO was homogeneously spread over the g-C3N4 surface. UV-vis diffuse reflectance spectroscopy analysis shows the slightly enhanced visible light absorption ability of the composite. Photoluminescence (PL) spectroscopy and electrochemical impedance spectroscopy analysis prove the higher charge separation of the composite during the irradiation of light. The composite shows admirable photocatalytic efficiency in the visible light-driven photocatalytic degradation of an aqueous diclofenac (DFC) solution. The superoxide anion radical (•O2 -) and hydroxyl radical (•OH) act as reactive species during the degradation reaction. Probable reaction mechanisms have been proposed.

Cellulose acetate membranes loaded with WO3/g-C3N4: a synergistic approach for effective photocatalysis

The objective of this study is to develop an efficient, easily recoverable membrane-based photocatalyst for removing organic pollutants from aqueous solutions. This study documents the effective synthesis of a novel composite photocatalyst comprising WO3/g-C3N4(WCN) loaded onto cellulose acetate (CA). The physicochemical properties of the synthesized nanocomposites were validated using a range of techniques, including Fourier transform infrared spectroscopy, x-ray diffraction, scanning electron microscopy (SEM), energy-dispersive x-ray spectroscopy, and UV-visible diffuse reflectance spectroscopy. SEM analysis revealed that the WCN particles exhibited a well-decorated arrangement on the CA surface in the form of spherical particles. The successfully synthesized film was utilized as a potential adsorbent for removing organic pollutants such as Rhodamine B (Rh-B) and Methylene blue (MB) from aqueous solutions under UV light illumination. The results showcased the significant potential of the WCN@CA nanocomposite, achieving a remarkable 83% and 85% efficiency in eliminating Rh-B and MB. The pseudo-first-order kinetic models were found to be appropriate for both dye adsorption onto the WCN@CA nanocomposite. The WCN@CA catalyst, capable of being reused five times without significant loss of efficiency, shows great potential for decomposing toxic organic pollutants. The novelty of this work lies in the innovative combination of WCN with CA, resulting in a highly efficient and reusable photocatalyst for environmental remediation.

Efficient removal of oxytetracycline antibiotic from aqueous media using UV/g-C3N4/Fe3O4 photocatalytic process

Residual pharmaceuticals in the environment are a class of emerging pollutants that endanger human health. Tetracycline's family, including oxytetracycline (OTC), are known as one of the most produced and consumed antibiotics worldwide. The g-C3N4/Fe3O4 nanocomposite with high level of catalytic efficiency features suitable performance in water/wastewater treatment. Therefore, in the present study, this nanocomposite was applied to remove the oxytetracycline from the aqueous environment. In this research study, g-C3N4/Fe3O4 nanocomposite (serving as catalyst) was initially synthesized by a simple hydrothermal method. The effect of key operating parameters such as initial solution pH, dose of catalyst, contact time and initial concentration of OTC in aqueous solutions was investigated under UV irradiation. In addition, COD and TOC tests, the kinetics and the effect of radical scavengers on the applied photocatalytic process were all evaluated. The maximum removal efficiency of OTC (99.8 %) was achieved under the following conditions: neutral solution pH 7; catalyst dose, 0.7 g/L; and an initial OTC concentration of 5 mg/L. The data showed that the kinetics of the reaction followed the first-order model with R2 of 0.9755. The respective COD and TOC efficiency values for the applied photocatalytic process were determined to be 87 and 59 %, respectively. In addition, the lowest removal efficiency of OTC was observed in the presence of tert-butanol radical scavengers, and OH radicals played a main role. The UV/g-C3N4/Fe3O4 photocatalytic process proved to be highly efficient for the removal of OTC antibiotic and could be potentially applied for the removal of other pollutants from aqueous solutions.

The development of ZnO nanoparticle-embedded graphitic-carbon nitride towards triple-negative breast cancer therapy

The present study deals with the effects of curcumin-loaded ZnO nanoparticles (NPs) embedded in graphitic-carbon nitride (g-C3N4) sheets for breast cancer cells. The synthesis of these sheets was carried out by a simple co-precipitation method. The physicochemical and thermal properties of the composite sheets were studied using various characterization techniques. The powder X-ray diffraction and high-resolution transmission electron microscopy analyses confirmed the hexagonal wurtzite phase of the ZnO nanoparticles, which were randomly distributed on the g-C3N4 nanosheets, generating a finely bonded interface between the two components. The X-ray photoelectron spectroscopy analysis confirmed the successful formation of the g-C3N4@ZnO composite, while the thermal studies revealed the thermal stability of the composite. In addition, the drug release and kinetics studies proved that the release of curcumin was more significant under acidic conditions (pH 5) compared with neutral pH (7.4). Further, the biological assays verified the antibacterial activity (against two different cultures of E. coli and S. aureus) and anticancer activity (against MDA-MB-231 cancer cells) of the g-C3N4@ZnO/C nanocomposite. Finally, the lactate dehydrogenase activity assay presented the cytotoxic assessment of the nanocomposite based on its cytoplasmic activity and the extent of enzymes released from the damaged cells.

Constructing C-O bridged CeO2/g-C3N4 S-scheme heterojunction for methyl orange photodegradation：Experimental and theoretical calculation

Owing to its feasibility, efficiency in light-harvesting and effectiveness in the interfacial charge transfer between two n-type semiconductors, constructing heterojunction photocatalysts have been identified as an effective way for enhancing the photocatalytic properties. In this research, a C-O bridged CeO₂/g-C₃N₄ (cCN) Step-scheme (S-scheme) heterojunction photocatalyst was constructed successfully. Under visible light irradiation, the cCN heterojunction exhibited the photocatalytic degradation efficiency of methyl orange, which was about 4.5 and 1.5 times higher than that of pristine CeO₂ and CN, respectively. The DFT calculations, XPS and FTIR analyses demonstrated the formation of C-O linkages. And the calculations of work functions revealed the electrons would flow from g-C₃N₄ to CeO₂ due to the difference in Fermi levels, resulting in the production of internal electric fields. Benefiting from the C-O bond and internal electric field, the photo-induced holes in the valence band of g-C₃N₄ and the photo-induced electrons from conduction band of CeO₂ would be recombined when exposed to visible light irradiation, while leaving the electrons with higher redox potential in the conduction band of g-C₃N₄. This collaboration accelerated the separation and transfer rate of photo-generated electron-hole pairs, which promoted the generation of superoxide radical (•O₂^-) and improved the photocatalytic activity.

One-Step Fabrication of the ZnO/g-C3N4 Composite for Visible Light-Responsive Photocatalytic Degradation of Bisphenol E in Aqueous Solution

The ZnO/g-C₃N₄ composite was successfully synthesized by a simple one-step calcination of a urea and zinc acetate mixture. The photocatalytic activity of the synthesized composite was evaluated in the degradation of bisphenol E (BPE). The morphology, crystallinity, optical properties, and composition of the synthesized composite were characterized by using various analytical techniques such as scanning electron microscopy (SEM), transmitted electron microscopy (TEM), field emission-electron probe microanalysis (FE-EPMA), nitrogen adsorption and desorption isotherm measurement, Fourier-transform infrared (FTIR) spectroscopy, X-ray powder diffraction (XRD), diffuse reflectance spectroscopy (DRS), photoluminescence (PL) spectroscopy, electrochemical impedance spectroscopy (EIS), X-ray photoelectron spectroscopy (XPS), and thermogravimetric analysis (TGA). The degradation rate of BPE with the ZnO/g-C₃N₄ composite was 8 times larger than that obtained with pure g-C₃N₄ at the optimal conditions. The excellent photocatalytic activity was attributed to the synergistic effect between the g-C₃N₄ and ZnO, which enhanced the efficiency of charge separations, reduced the e^-/h⁺ pairs recombination, and increased the visible light absorption ability. The radical scavenger studies indicated that the ^•O₂ ^- and h⁺ species were mainly responsible for the degradation of BPE. The stability test suggested the chemical and photostability of the synthesized composite. Two possible photocatalytical mechanisms have been suggested.

Peroxymonosulfate enhanced photoelectrocatalytic oxidation of organic contaminants and simultaneously cathodic recycling of silver

Degradation of organic contaminants with simultaneous recycling of Ag⁺ from silver-containing organic wastewater such as photographic effluents is desired. Although photoelectrocatalysis (PEC) technology is a good candidate for this type of wastewater, its reaction kinetics still needs to be improved. Herein, peroxymonosulfate (PMS) was employed to enhance the PEC kinetics for oxidation of phenol (PhOH) at the anode and reduction of Ag⁺ at the cathode. The degradation efficiency of phenol (PhOH, 0.1 mmol/L) was increased from 42.8% to 96.9% by adding 5 mmol/L PMS at a potential of 0.25 V. Meanwhile, the Ag (by wt%) deposited on the cathode was 28.1% (Ag₂O) in PEC process, while that of Ag (by wt%) was 69.7% (Ag⁰) by adding PMS. According to the electrochemistry analysis, PMS, as photoelectrons acceptor, enhances the separation efficiency of charges and the direct h⁺ oxidation of PhOH at the photoanode. Meantime, the increasing cathode potential avoided H₂ evolution and strongly alkaline at the surface of cathode, thus enabling the deposition of Ag⁺ in the form of metallic silver with the help of PMS. In addition, PMS combined with PEC process was effective in treating photographic effluents.

Enhanced Photoelectrocatalytic Activity of TiO2 Nanowire Arrays via Copolymerized G-C3N4 Hybridization

Photoelectrocatalytic (PEC) oxidation is an advanced technology that combines photocatalytic oxidation (PC) and electrolytic oxidation (EC). PEC activity can be greatly enhanced by the PC and EC synergy effect. In this work, novel copolymerized g-C3N4 (denoted as CNx)/TiO2 core-shell nanowire arrays were prepared by chemical vapor deposition. CNx were deposited on the surface of TiO2 nanowire arrays using organic monomer 4,5-dicyanidazole and dicyandiamide as copolymerization precursor. TiO2 nanowire arrays provide a direct and fast electron transfer path, while CNx is a visible light responsive material. After CNx deposition, the light response range of TiO2 is broadened to 600 nm. The deposition of CNx shell effectively improves the PC efficiency and PEC efficiency of TiO2. Under visible light irradiation and 1 V bias potential, the rate constant k of PEC degradation of CNx/TiO2 core-shell nanowire arrays is 0.0069 min−1, which is 72% higher than that of pure TiO2 nanowires. The built-in electric field formed in the interface between TiO2 core and CNx shell would effectively promote photogenerated charge separation and PEC activity.

The Preparation of g-C3N4/CoAl-LDH Nanocomposites and Their Depollution Performances in Cement Mortars under UV-Visible Light

In this study, new organic-inorganic g-C3N4/CoAl-LDH nanocomposites were prepared and introduced to fabricate photocatalytic cement mortars by internal mixing, coating, and spraying. The photocatalytic depollution of both g-C3N4/CoAl-LDH and cement mortars was assessed by NOx degradation reaction under UV-visible light irradiation. The study results suggested that the degradation efficiency of g-C3N4/CoAl-LDH nanocomposites improved with an increase in g-C3N4 content. The g-C3N4/CoAl-LDH1.5 nanocomposite displayed the highest NOx degradation capacity, which was about 1.23 and 3.21 times that of pure g-C3N4 and CoAl-LDH, respectively. The photocatalytic cement mortars which were all fabricated using different approaches could effectively degrade the target pollutants and exhibited significant compatibility between g-C3N4/CoAl-LDH and cementitious substrate. Among them, the coated mortars showed strong resistance to laboratory-simulated wearing and abrasion with a small decrease in degradation rate.

A Comprehensive Review of Graphitic Carbon Nitride (g-C3N4)-Metal Oxide-Based Nanocomposites: Potential for Photocatalysis and Sensing

g-C3N4 has drawn lots of attention due to its photocatalytic activity, low-cost and facile synthesis, and interesting layered structure. However, to improve some of the properties of g-C3N4, such as photochemical stability, electrical band structure, and to decrease charge recombination rate, and towards effective light-harvesting, g-C3N4-metal oxide-based heterojunctions have been introduced. In this review, we initially discussed the preparation, modification, and physical properties of the g-C3N4 and then, we discussed the combination of g-C3N4 with various metal oxides such as TiO2, ZnO, FeO, Fe2O3, Fe3O4, WO3, SnO, SnO2, etc. We summarized some of their characteristic properties of these heterojunctions, their optical features, photocatalytic performance, and electrical band edge positions. This review covers recent advances, including applications in water splitting, CO2 reduction, and photodegradation of organic pollutants, sensors, bacterial disinfection, and supercapacitors. We show that metal oxides can improve the efficiency of the bare g-C3N4 to make the composites suitable for a wide range of applications. Finally, this review provides some perspectives, limitations, and challenges in investigation of g-C3N4-metal-oxide-based heterojunctions.

The CdS/g-C3N4 nano-photocatalyst: Brief characterization and kinetic study of photodegradation and mineralization of methyl orange

The CdS/g-C₃N₄ hybrid was prepared mechanically and characterized by different techniques including XRD, SEM, DRS, FTIR, and cyclic voltammetry (CV). The SEM study showed that CdS nanoparticles (NPs) have been randomly dispersed on the surface of graphitic carbon nitride (g-C₃N₄). The CV results showed better charge carriers' transfer for the modified carbon paste electrode (CPE) by the CdS/g-C₃N₄ system concerning the modified CPE by single CdS or g-C₃N₄ modifier. The band gap (Bg) energies of 1.7, 2.7, and 1.9 eV were obtained from DRS results for CdS, g-C₃N₄, and CdS/g-C₃N₄ systems, respectively. The photocatalytic activity of the single and hybrid systems was tested towards methyl orange (MO). The degradation extents of 16%, 22%, and 34% were respectively obtained for CdS NPs, g-C₃N₄, and CdS/g-C₃N₄ systems at initial steps. To enhance the degradation efficiency, the mole ratio of the component was changed in the second step. The work was then focused on the kinetic study of both photodegradation and mineralization processes. For this goal, the degradation extents of the photodegraded MO solutions were calculated based on the recorded absorbance of the solutions in the visible-light and the results were then subjected to the Hinshelwood equation. Then the solutions were subjected to COD experiment to follow the mineralization extent of MO. Form the slopes of the Hinshelwood plots, the rate constants of 0.024 and 0.025 min^-1 were obtained for the degradation and mineralization of MO molecules, respectively. TOC results confirmed the mineralization of 187.5 μmoles of MO molecules in a 50 ppm MO solution.

Facile One-Pot Biogenic Synthesis of Cu-Co-Ni Trimetallic Nanoparticles for Enhanced Photocatalytic Dye Degradation

Biomolecules from plant extracts have gained significant interest in the synthesis of nanoparticles owing to their sustainable properties, cost efficiency, and environmental wellbeing. An eco-friendly and facile method has been developed to prepare Cu-Co-Ni trimetallic nanoparticles with simultaneous bio-reduction of Cu-Co-Ni metal precursors by aqueous extract of oregano (Origanum vulgare) leaves. Dramatic changes in physicochemical properties of trimetallic nanoparticles occur due to synergistic interactions between individual metal precursors, which in turn outclass the properties of corresponding monometallic nanoparticles in various aspects. The as biosynthesized Cu-Co-Ni trimetallic nanoparticles were initially analyzed using ultraviolet (UV)–visible spectroscopy. The morphology, structure, shape, and size of biosynthesized trimetallic nanoparticles were confirmed by transmission electron microscopy (TEM), scanning electron microscopy (SEM), and X-ray diffraction (XRD) spectroscopy. The elemental analysis was carried out by energy-dispersive X-ray (EDX) spectroscopy. Fourier transform infrared (FTIR) microscopy was carried out to explain the critical role of the biomolecules in the Origanum vulgare leaf extract as capping and stabilizing agents in the nanoparticle formation. Additionally, simultaneous thermogravimetric analysis (TGA) and differential thermogravimetry (DTG) analysis was also performed to estimate the mass evaluation and rate of the material weight changes. The photocatalytic activity of as biosynthesized trimetallic nanoparticles was investigated towards methylene blue (MB) dye degradation and was found to be an efficient photocatalyst for dye degradation. Kinetic experiments have shown that photocatalytic degradation of MB dye followed pseudo-first-order kinetics. The mechanism of the photodegradation process of biogenic Cu-Co-Ni trimetallic nanoparticles was also addressed.

Synergistic adsorption-photocatalytic degradation effect and norfloxacin mechanism of ZnO/ZnS@BC under UV-light irradiation

Norfloxacin (NOF) is an environmentally harmful and ubiquitous aquatic pollutant with extensive production and application. In this study, a novel composition named carbon-based composite photocatalytic material of zinc oxide and zinc sulphide (ZnO/ZnS@BC) was successfully obtained by the impregnation-roasting method to remove NOF under UV-light. Scanning electron microscopy, X-ray photoelectron spectroscopy, transmission electron microscopy and energy dispersive spectrometer characterised the composition. ZnO/ZnS was successfully decorated on the surface of biochar (BC). The pH, the ZnSO₄/PS ratio, and ions and quenchers, were investigated. High removal efficiency was obtained with a pH of 7 and a ZnSO₄/PS ratio of 1:1, and the removal ratio of NOF reached 95% within three hours; the adsorption and degradation ratios reached 46% and 49%, respectively. Fe²⁺ promoted the degradation of NOF, whereas other ions inhibited it, with NO₃^- showing the strongest inhibitory effect. Three reactive species (tert-butanol, quinone, and ammonium oxala) were identified in the catalytic system. The decreasing order of the contribution of each reactive species was: O₂^- > ·OH^- > h⁺. Additionally, a recycling experiment demonstrated the stability of the catalyst; the catalytic degradation ratio of NOF reached 78% after five successive runs. Therefore, ZnO/ZnS@BC possessed strong adsorption capacity and high ultraviolet photocatalysis ability.

Effects of defects in g-C3N4 on excited-state charge distribution and transfer: Potential for improved photocatalysis

Graphite phase carbon nitride (g-C₃N₄) with triazine ring structures is a polymeric metal-free semiconductor with a medium bandgap and two-dimensional layered structure. g-C₃N₄ has attracted attention because of its photocatalytic applications, such as the photodegradation of pollution and hydrogen production via water splitting. Defective elements and sites are two essential factors in rationally designing highly-efficient photocatalysts based on g-C₃N₄ at the nanoscale. When the molecule absorbs energy and enters an excited state, electrons migrate and the charge distribution changes accordingly. The properties of the excited states of g-C₃N₄ are related to its defect elements and sites. Therefore, it is necessary to understand the effects of defects on excited states in the design of g-C₃N₄ catalysts. In this paper, the excited-state characteristics of intrinsic g-C₃N₄ and g-C₃N₄ with C- and N-atom defects are analyzed by density functional theory. We apply quantum chemistry and wave function analysis to determine the hole-electron distributions and charge transfer directions. To measure and discuss the characteristics of electron excitation using quantitative numerical methods, the D, Sr, H, and t indices are calculated. Our results promote a deeper understanding of the roles of defective elements and sites in photocatalysis by g-C₃N₄.

Accessing the rich carbon nitride materials chemistry by heat treatments of ammonium thiocyanate, NH4SCN

Carbon nitride materials include functional materials, and their chemical diversity and complexity are becoming increasingly appreciated. Heating of NH₄SCN leads to a range of new carbon nitride compounds, which have been structurally characterized by single-crystal X-ray diffraction. Heating at ambient pressure to 175°C leads to guanidinium thiocyanate, H₆CN₃SCN (1), and when maintaining that temperature for about 12 h a water-insoluble carbon nitride product is formed, which is a co-crystal between melamine and melamium thiocyanate, [H₆C₃N₆]·[H₁₀C₆N₁₁]⁺·[SCN]^- (2). In situ powder X-ray diffraction measurements of this material reveal a gradual transformation from (2), via two intermediate products, to a final melon-like end product. The first of these forms between 350 and 400°C, and is an adduct of melam and melamium thiocyanate, [H₉C₆N₁₁]·2[H₁₀C₆N₁₁]⁺·2[SCN]^- (3). The second forms between 400 and 480°C, and is identified as melem, 2,5,8-triamino-tri-s-triazine, H₆C₆N₁₀ (4). On heating of (2) in a sealed ampoule to 600°C, various crystals were obtained and six crystal structures were determined from the batch: 1,3,5-triazine-2,4,6-triamino, H₆C₃N₆ (5), 1,3,5-triazine-2,4-diamino, H₅C₃N₅ (6), 1,1',3,3',5,5'-triazine-2,2',4,4'-tetraamino, H₈C₆N₁₀ (7), 2[H₆C₃N₆]·[H₁₀C₆N₁₁]⁺·[SCN]^- (8) and 2[H₆C₃N₆]·[H₇C₃N₆]⁺·[SCN]^- (9). Finally, a recrystallized decomposition product was found to be [H₆C₃N₆]·[H₇C₃N₆]⁺·[SCN]^-·[H₂O] (10).

Photocatalytic Degradation of 2,4,6-Trichlorophenol by MgO–MgFe2O4 Derived from Layered Double Hydroxide Structures

In recent years, the search for solutions for the treatment of water pollution by toxic compounds such as phenols and chlorophenols has been increasing. Phenols and their derivatives are widely used in the manufacture of pesticides, insecticides, paper, and wood preservers, among other things. Chlorophenols are partially biodegradable but not directly photodegradable by sunlight and are extremely toxic—especially 2,4,6-trichlorophenol, which is considered to be potentially carcinogenic. As a viable proposal to be applied in the treatment of water contaminated with 2,4,6-trichlorophenol, this paper presents an application study of the thermally activated Mg/Fe layered double hydroxides as photocatalysts for the mineralization of this contaminant. Activated Mg/Fe layered double hydroxides were characterized by X-ray diffraction, thermal analysis, N2 physisorption, and scanning electron microscopy with X-ray dispersive energy. The results of the photocatalytic degradation of 2,4,6-trichlorophenol in aqueous solution showed good photocatalytic activity, with an efficiency of degradation of up to 93% and mineralization of 82%; degradation values which are higher than that of TiO2-P25, which only reached 18% degradation. The degradation capacity is attributed to the structure of the MgO–MgFe2O4 oxides derived from double laminate hydroxide Mg/Fe. A path of degradation based on a mechanism of superoxide and hollow radicals is proposed.

Photodegradation of fluazaindolizine in aqueous solution with graphitic carbon nitride nanosheets under simulated sunlight illumination

The photodegradation of fluazaindolizine (FZDL) under simulated sunlight irradiation was accelerated by the catalysis of graphitic carbon nitride (g-C₃N₄). Under optimum conditions, such as 5 mg of amount and dispersion, the photodegradation half-life was dramatically enhanced to 2.7 h. More importantly, the pathway of degradation by g-C₃N₄ was different from both direct photolysis and the catalysis by titanium oxide, with particular negative ions of m/z 221 and 195, corresponding to the cleavage of sulfamide bond and the ring opening of imidazole, respectively. In addition, hydroxyl and superoxide radicals played important roles in photodegradation. The results enriched not only the study of FZDL photodegradation but also the application of g-C₃N₄. It also suggested the possibility of the water purification by photodegradation for pesticide removal in real life.

In-Situ Fabrication of g-C₃N₄/ZnO Nanocomposites for Photocatalytic Degradation of Methylene Blue: Synthesis Procedure Does Matter

The nanocomposite preparation procedure plays an important role in achieving a well-established heterostructured junction, and hence, an optimized photocatalytic activity. In this study, a series of g-C₃N₄/ZnO nanocomposites were prepared through two distinct procedures of a low-cost, environmentally-friendly, in-situ fabrication process, with urea and zinc acetate being the only precursor materials. The physicochemical properties of synthesized g-C₃N₄/ZnO composites were mainly characterized by XRD, UV–VIS diffuse reflectance spectroscopy (DRS), N₂ adsorption-desorption, FTIR, TEM, and SEM. These nanocomposites’ photocatalytic properties were evaluated in methylene blue (MB) dye photodecomposition under UV and sunlight irradiation. Interestingly, compared with ZnO nanorods, g-C₃N₄/ZnO nanocomposites (x:1, obtained from urea and ZnO nanorods) exhibited weak photocatalytic activity likely due to a “shading effect”, while nanocomposites (x:1 CN, made from g-C₃N₄ and zinc acetate) showed enhanced photocatalytic activity that can be ascribed to the effective establishment of heterojunctions. A kinetics study showed that a maximum reaction rate constant of 0.1862 min^-1 can be achieved under solar light illumination, which is two times higher than that of bare ZnO nanorods. The photocatalytic mechanism was revealed by determining reactive species through adding a series of scavengers. It suggested that reactive ●O₂⁻ and h⁺ radicals played a major role in promoting dye photodegradation.

Activation of peroxymonosulfate by BiOCl@Fe3O4 catalyst for the degradation of atenolol: Kinetics, parameters, products and mechanism

BiOCl@Fe₃O₄ photocatalyst was synthesized to activate peroxymonosulfate (PMS) for atenolol (ATL) degradation under simulated sunlight irradiation in present study. XRD, SEM, adsorbability and pore size distribution of BiOCl@Fe₃O₄ were analyzed. Magnetic BiOCl performed high activity in PMS activation and could be easily solid-liquid separation by applying an external magnetic field. Many parameters were inspected, including scavengers, PMS concentration, catalyst dosage, pH, anions (Cl^- and CO₃^-). h⁺, SO₄^-, HO, O₂^-, SO₅^- were involved in ATL degradation in BiOCl@Fe₃O₄/PMS/sunlight system. The second-order rate constant of the reaction between ATL and SO₄^- (k_ATL, _SO4-) was estimated via laser flash photolysis experiments. Moreover, ATL mineralization was followed by TOC analyzer. Twelve possible intermediate products were identified through LC-QTOF-MS analysis, and six ATL degradation pathways were concluded. This type of magnetic photocatalyst is characterized by ease of separation, high activation and good reusability. It may have application potential in refractory organic pollutants degradation.

Enhanced Visible Light Photocatalytic Reduction of Cr(VI) over a Novel Square Nanotube Poly(Triazine Imide)/TiO2 Heterojunction

Hexavalent chromium Cr(VI) pollution makes has a harmful impact on human health and the ecological environment. Photocatalysis reduction technology exhibits low energy consumption, high reduction efficiency and stable performance, and is playing an increasingly important role in chromium pollution control. Graphite-phase carbon nitride has been used to reduce Cr(VI) to the less harmful Cr(III) due to its visible light catalytic activity, chemical stability and low cost. However, it has a low specific surface area and fast recombination of electron–hole pairs, which severely restrict its practical application. In this work, a TiO2-modified poly(triazine imide) (PTI) square nanotube was prepared by the one-step molten salts method. The results showed the PTI had a square hollow nanotube morphology, with an about 100–1000 nm width and 60–70 nm thickness. During the formation of the PTI square tube, TiO2 nanoparticles adhere to the surface of the square tube wall by strong adsorption, and eventually form a PTI/TiO2 heterojunction. The PTI/TiO2-7 wt% heterojunction exhibited very good Cr(VI) reduction efficiency within 120 min. The enhanced photocatalytic activity was mainly attributed to the efficient separation and transport of photo-induced electron–hole pairs and the high specific surface area in the heterojunction structure.

ZnO nanorod arrays grown on g-C3N4 micro-sheets for enhanced visible light photocatalytic H2 evolution

The designed synthesis of noble-metal-free photocatalysts with hierarchical heteroassemblies in a facile, mild and eco-friendly way becomes more and more important, because we can explore the novel properties and applications of novel heterostructures via this method. Herein we report a two-step aqueous strategy for novel hierarchical heterostructures of ZnO nanorod (NR) arrays grown on graphitic carbon nitride (g-C₃N₄). The novel g-C₃N₄/ZnO NR heterostructures that integrate g-C₃N₄ and ZnO NR via high-quality g-C₃N₄–ZnO heterojunctions have beneficial properties such as high specific surface area (SSA), open spatial architecture, good electronic conductivity, and effective charge transfer interfaces, and are promising in many related areas such as water splitting, solar cells, etc. As a noble-metal-free and visible-light-responsive photocatalytic material, a typical g-C₃N₄/ZnO NR photocatalytic system exhibits enhanced photocatalytic activity toward H₂ evolution, almost 3.5 times higher than that of pure g-C₃N₄. The superior photocatalytic property can be ascribed to the synergistic effect of the unique g-C₃N₄/ZnO NR heterostructures.

The designed synthesis of photocatalysts with hierarchical heteroassemblies in a facile, mild and eco-friendly way becomes more and more important, since we can explore the novel properties and applications of novel heterostructures via this method.

Structures and energetics of low-index stoichiometric BiPO4surfaces

Four low-index surfaces of monazite BiPO₄in the Wulff shape are investigated.

Efficient enhancement of ozonation performance via ZVZ immobilized g-C3N4 towards superior oxidation of micropollutants

A functional organic-metal composite material zero-valent zinc immobilized graphitic carbon nitride (ZVZ-g-C₃N₄) was prepared by a fast and facile two-step synthetic approach with an optimal ZVZ content of 5.4 wt%. The structure, surface morphology and chemical composition of the as-synthesized ZVZ-g-C₃N₄ were characterized by BET surface area, XRD, FT-IR, SEM, TEM, and XPS, respectively. ZVZ-g-C₃N₄ composite exhibited superior catalytic ozonation activity with an improvement of 61.2% on atrazine (ATZ) degradation efficiency in 1.5 min reaction, more than 12 times of the pseudo-first-order rate constant, and almost 16-fold of the R_ct value obtained in O₃/ZVZ-g-C₃N₄ process compared to O₃ alone. Meanwhile, the ATZ degradation efficiency was gradually enhanced with increasing ZVZ-g-C₃N₄ dosage and initial solution pH in the range from 3.0 to 9.0, and a higher amount of ATZ was degraded when the initial concentration of ATZ rose from 1 to 10 mg L^-1. The enhanced catalytic ozonation activity of ZVZ-g-C₃N₄ is attributed to the synergistic effects among ZVZ, ZnO and g-C₃N₄, as well as the improved dispersibility, increased surface area, and intensive electron-transfer ascribed to the electronic and surface properties modification. The radical scavengers experiments demonstrated that O₂^-, OH, and ¹O₂ were the dominant reactive radical species in the multifunctional processes. Moreover, an empirical kinetic model was proposed to predict ATZ degradation. The results indicated that the ZVZ-g-C₃N₄ composite was a highly efficient, recoverable, and durable catalyst, which would provide a promising alternative in catalytic ozonation.

Degradation of atenolol via heterogeneous activation of persulfate by using BiOCl@Fe3O4 catalyst under simulated solar light irradiation

Efficient oxidative degradation of pharmaceutical pollutants in aquatic environments is of great importance. This study used magnetic BiOCl@Fe₃O₄ catalyst to activate persulfate (PS) under simulated solar light irradiation. This degradation system was evaluated using atenolol (ATL) as target pollutant. Four reactive species were identified in the sunlight/BiOCl@Fe₃O₄/PS system. The decreasing order of the contribution of each reactive species on ATL degradation was as follows: h⁺ ≈ HO^· > O₂^·- > SO₄^·-. pH significantly influenced ATL degradation, and an acidic condition favored the reaction. High degradation efficiencies were obtained at pH 2.3-5.5. ATL degradation rate increased with increased catalyst and PS contents. Moreover, ATL mineralization was higher in the sunlight/BiOCl@Fe₃O₄/PS system than in the sunlight/BiOCl@Fe₃O₄ or sunlight/PS system. Nine possible intermediate products were identified through LC-MS analysis, and a degradation pathway for ATL was proposed. The BiOCl@Fe₃O₄ nanomagnetic composite catalyst was synthesized in this work. This catalyst was easily separated and recovered from a treated solution by using a magnet, and it demonstrated a high catalytic activity. Increased amount of the BiOCl@Fe₃O₄ catalyst obviously accelerated the efficiency of ATL degradation, and the reusability of the catalyst allowed the addition of a large dosage of BiOCl@Fe₃O₄ to improve the degradation efficiency.

2D graphitic-C3N4 hybridized with 1D flux-grown Na-modified K2Ti6O13 nanobelts for enhanced simulated sunlight and visible-light photocatalytic performance

Novel 1D/2D hybrid Na-K₂Ti₆O₁₃/g-C₃N₄ heterojunction photocatalysts with enhanced simulated sunlight and visible-light photocatalytic performance have been successfully fabricated using a facile mixing–calcination method.