Rationally Designed S-Scheme CeO2/g-C3N4 Heterojunction for Promoting Visible Light Driven CO2 Photoreduction into Syngas

Exploring low-cost visible light photocatalysts for CO2 reduction to produce proportionally adjustable syngas is of great significance for meeting the needs of green chemical industry. A S-Scheme CeO2/g-C3N4 (CeO2/CN) heterojunction was constructed by using a simple two-step calcination method. During the photocatalytic CO2 reduction process, the CeO2/CN heterojunction can present a superior photocatalytic performance, and the obtained CO/H2 ratios in syngas can be regulated from 1 : 0.16 to 1 : 3.02. In addition, the CO and H2 production rate of the optimal CeO2/CN composite can reach 1169.56 and 429.12 μmol g-1 h-1, respectively. This superior photocatalytic performance is attributed to the unique S-Scheme photogenerated charge transfer mechanism between CeO2 and CN, which facilitates rapid charge separation and migration, while retaining the excellent redox capacity of both semiconductors. Particularly, the variable valence Ce3+/Ce4+ can act as electron mediator between CeO2 and CN, which can promote electron transfer and improve the catalytic performance. This work is expected to provide a new useful reference for the rational construction of high efficiency S-Scheme heterojunction photocatalyst, and improve the efficiency of photocatalytic reduction of CO2, promoting the photocatalytic reduction of CO2 into useful fuels.

One-pot synthesis of g-C3N4/N-doped CeO2 nanocomposites and their potential visible light-driven photocatalytic degradation of methylene blue dye

In the pursuit of efficient photocatalytic materials for environmental applications, a new series of g-C3N4/N-doped CeO2 nanocomposites (g-C3N4/N-CeO2 NCs) was synthesized using a straightforward dispersion method. These nanocomposites were systematically characterized to understand their structural, optical, and chemical properties. The photocatalytic performance of g-C3N4/N-CeO2 NCs was evaluated by investigating their ability to degrade methylene blue (MB) dye, a model organic pollutant. The results demonstrate that the integration of g-C3N4 with N-doped CeO2 NCs reduces the optical energy gap compared to pristine N-doped CeO2, leading to enhanced photocatalytic efficiency. It is benefited from the existence of g-C3N4/N-CeO2 NCs not only in promoting the charge separation and inhibits the fast charge recombination but also in improving photocatalytic oxidation performance. Hence, this study highlights the potential of g-C3N4/N-CeO2 NCs as promising candidates for various photocatalytic applications, contributing to the advancement of sustainable environmental remediation technologies.

Photocatalytic Efficiency for CO2 Reduction of Co and Cluster Co2O2 Supported on g-C3N4: A Density Functional Theory and Machine Learning Study

It is well known from experimental results that a single atom of cobalt supported on g-C3N4 is an efficient photocatalyst for the reduction of CO2 to CO, with a better photocatalytic activity than g-C3N4. In this work, we investigate the performance as catalysts for the CO2 reduction of single atoms of cobalt and Co2O2 clusters supported on graphitic carbon nitride (g-C3N4). Employing density functional theory plus Hubbard (DFT + U) calculations, we investigate in detail the reduction mechanisms to CO and HCOOH for the first time. We find that deposition of cobalt on g-C3N4 decreases the work function of g-C3N4 to 6.6 eV and provides a better candidate for the reduction reaction. In addition, we find that the preferred product of CO2 reduction on Co@g-C3N4 is CO, with a rate-determining barrier of 0.97 eV, while on Co2O2@g-C3N4, CO2 reduces to formate with a rate-determining barrier of 0.44 eV. We determine the creation of CO2 from COOH to only take place on Co2O2@g-C3N4, with a (relatively high) barrier of 2.27 eV. In order to obtain more easily the transition state energies of the reactions mentioned above, we applied machine learning methods to search for high-importance descriptors for these quantities, in the case of single transition metal atoms supported on C3N4. Interestingly, our results show that our quantities of interest are closely related to the adsorption energies of products and normalized valence electrons of the products of the elementary reactions as well as those of the metal atoms. The former of these two sets of features can be straightforwardly obtained via DFT, while the latter energies are extensively tabulated. Our results offer guidance for the design of catalysts and photocatalysts for CO2 reduction on single-metal atoms supported on C3N4.

Proceeding of catalytic water splitting on Cu/Ce@g-C3N4 photocatalysts: an exceptional approach for sunlight-driven hydrogen generation

Increasing energy demands and environmental problems require carbon-free and renewable energy generation systems. For this purpose, we have synthesized efficient photocatalysts (i.e., g-C3N4, Cu@g-C3N4, Ce@g-C3N4 and Cu/Ce@g-C3N4) for H2 evolution from water splitting. Their optical, structural and electrochemical properties were investigated by UV-Vis-DRS, PL, XRD, FTIR, Raman and EIS methods. Their surface morphologies were evaluated by AFM and SEM analyses. Their chemical characteristics, compositions and stability were assessed using XPS, EDX and TGA techniques. Photoreactions were performed in a quartz reactor (150 mL/Velp-UK), whereas hydrogen generation activities were monitored using a GC-TCD (Shimadzu-2014/Japan). The results depicted that Cu/Ce@g-C3N4 catalysts are the most active catalysts that deliver 23.94 mmol g-1 h-1 of H2. The higher rate of H2 evolution was attributed to the active synergism between Ce and Cu metals and the impact of surface plasmon electrons (SPEs) of Cu that were produced during the photoreaction. The rate of H2 production was optimized by controlling various factors, including the catalyst amount, light intensity, pH, and temperature of the reaction mixture. It has been concluded that the current study holds promise to replace the conventional and costly catalysts used for hydrogen generation technologies.

Enriched photocatalytic and photoelectrochemical activities of a 2D/0D g-C3N4/CeO2 nanostructure

Sunlight-powered photocatalysts made from CeO2 nanosized particles and g-C3N4 nanostructures were produced through a thermal decomposition process with urea and cerium nitrate hexahydrate. The preparation of g-C3N4, CeO2, and a binary nanostructured g-C3N4/CeO2 photocatalyst was done through a facile thermal decomposition method. The structural properties were analyzed using powder X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, energy dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy (XPS). Photocatalyst properties were characterized by using crystal violet (CV), a UV-Vis spectrophotometer, photocurrent and electron impedance spectroscopy (EIS). The structural and morphological analyses revealed that the g-C3N4/CeO2 nanostructures significantly enhanced the photoactivity for CV dye degradation under simulated sunlight, with a degradation rate of 94.5% after 105 min, compared to 82.5% for pure g-C3N4 and 45% for pure CeO2. This improvement was attributed to the noticeable visible light absorption and remarkable charge separation abilities of the nanostructures. Additionally, the g-C3N4/CeO2 nanostructures showed notable PEC performance under simulated sunlight. This study presents an easy and efficient method for producing g-C3N4 photocatalysts decorated with semiconductor materials and provides insights for designing nanostructures for photocatalytic and energy applications.

Photocatalytic dye degradation and antibacterial activities of CeO2/g-C3N4 nanomaterials for environmental applications

The uncontrolled dumping of synthetic dyes into water sources has posed severe hazards to the ecosystem. For decades, several materials with low cost and high efficiency have been investigated for dye degradation. Photocatalytic degradation is regarded as a successful strategy since it utilizes sunlight to transform harmful pollutants into nontoxic compounds without using oxidative agents. The photocatalytic potentials of CeO2/g-C3N4 (CG) were investigated in this work using a simplistic ultrasonication process. Here, the amount of CeO2 was fixed, and g-C3N4 was varied in the ratio (1:x, where x = 1, 2, and 3) and abbreviated as CG1, CG2, and CG3. Characterization techniques such as Fourier transforms-infrared spectroscopy, thermal gravimetric analysis (TGA), powdered X-ray diffraction, ultraviolet-visible spectroscopy, etc. were used to characterize structural analysis, optical properties, particle size, and chemical bonds of the prepared nanocomposites. The photocatalytic results showed that CG2 effectively degraded rose bengal (RB) and crystal violet (CV) dyes when exposed to visible light irradiation as compared to pure GCN and CeO2. The antibacterial activity analysis further supported the potential application of prepared photocatalyst as a disinfectant agent against both gram-positive (Staphylococcus aureus and Bacillus cereus) and gram-negative (Salmonella abony and Escherichia coli) pathogenic strains of bacteria.

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.

Rational Design of Monolithic g-C3N4 with Floating Network Porous-like Sponge Monolithic Structure for Boosting Photocatalytic Degradation of Tetracycline under Simulated and Natural Sunlight Illumination

In order to solve the problems of powder g-C₃N₄ catalysts being difficult to recycle and prone to secondary pollution, floating network porous-like sponge monolithic structure g-C₃N₄ (FSCN) was prepared with a one-step thermal condensation method using melamine sponge, urea, and melamine as raw materials. The phase composition, morphology, size, and chemical elements of the FSCN were studied using XRD, SEM, XPS, and UV-visible spectrophotometry. Under simulated sunlight, the removal rate for 40 mg·L^-1 tetracycline (TC) by FSCN reached 76%, which was 1.2 times that of powder g-C₃N₄. Under natural sunlight illumination, the TC removal rate of FSCN was 70.4%, which was only 5.6% lower than that of a xenon lamp. In addition, after three repeated uses, the removal rates of the FSCN and powder g-C₃N₄ samples decreased by 1.7% and 2.9%, respectively, indicating that FSCN had better stability and reusability. The excellent photocatalytic activity of FSCN benefits from its three-dimensional-network sponge-like structure and outstanding light absorption properties. Finally, a possible degradation mechanism for the FSCN photocatalyst was proposed. This photocatalyst can be used as a floating catalyst for the treatment of antibiotics and other types of water pollution, providing ideas for the photocatalytic degradation of pollutants in practical applications.

Rational optimization of g-C3N4/Co3O4 nanocomposite for enhanced photodegradation of Rhodamine B dye under visible light

Heterogeneous catalysis is widely known as an efficient, clean, and low-cost technology to mitigate the environmental pollution of industrial effluents. This research aimed at optimizing the preparation and characterization of efficient g-C₃N₄/Co₃O₄ nanocomposite for catalytic removal of Rhodamine B (Rh B) dye. The detected XRD peaks for the prepared nano-Co₃O₄ are matched with the cubic crystal structure. In contrast, the broad peak at 27.3° corresponding to the graphite reflection of hkl (002) was noticeably weakened in the XRD pattern of the g-C₃N₄/Co₃O₄ composite. FTIR spectra of g-C₃N₄/Co₃O₄ nanocomposites revealed the active vibrational modes of each Co₃O₄ and g-C₃N₄ component. The microstructure study of g-C₃N₄ showed the strong interlayer stacking of carbon nitride nanosheets, while the surface morphology of g-C₃N₄/Co₃O₄ nanocomposite revealed a hybrid particulate system. EDS analysis indicated that the spot area of g-C₃N₄/Co₃O₄ confirmed the chemical ratios of carbon, nitrogen, cobalt, and oxygen. BET measurements of g-C₃N₄/Co₃O₄ showed a significant increase in the surface area and pore volume of single components due to the lamination of stacked g-C₃N₄ nanosheets by the intercalated Co₃O₄ nanoparticles. The prepared 30% g-C₃N₄/Co₃O₄ revealed the lowest value of E_g ~1.2 eV and the highest light absorptivity suggesting strong promotion for the photocatalytic performance under visible light. The maximum photocatalytic activity of about 87% was achieved by 30% g-C₃N₄/Co₃O₄ due to the photonic enhancement, which reduces the recombination of excited electrons. The developed nanocomposite with a g-C₃N₄/Co₃O₄ ratio of 0.3 exhibited high stability in its photocatalytic performance after four recycling times, and a slight decrease of about 7% was estimated after the 5th reuse test.

Solar-light-driven photocatalytic degradation of pharmaceutical pollutants utilizing 2D g-C3N4/BiOCl composite

Pharmaceuticals, which have been praised for protecting countless lives, have become a new category of environmental pollutants in recent decades as most of these pharmaceutical compounds are discovered in water bodies in concentrations ranging from ng/L to mg/L. Recently, metal-free g-C₃N₄ (GCN)-based composites have received considerable attention for the degradation of pharmaceutical compounds. In this study, GCN/BiOCl composite was prepared using a simple ultrasonication-assisted stirring method and characterized using various analytical and spectroscopic techniques including XRD, FTIR, PL, Elemental mapping, UV-DRS, FESEM, HRTEM, and TGA. The as-prepared composite was utilized to degrade levofloxacin (LVX) under solar light irradiation and showed excellent stability for the degradation of LVX. Furthermore, the universality of the GCN/BiOCl composite was investigated by degrading diverse pharmaceuticals such as ofloxacin (OFX), norfloxacin (NOX), ciprofloxacin (COX), and ketorolac tromethamine (KTC) in an aqueous phase. Therefore, this work provides an effective method to degrade pharmaceutical contaminants simultaneously in water using GCN/BiOCl composite.

Polymeric graphitic carbon nitride layers decorated with erbium oxide and enhanced photocatalytic performance under visible light irradiation

Developing and implementing visible light active organic-inorganic hybrid semiconductor nanomaterials with enhanced photocatalytic properties find newer environmental and energy treatment capabilities. Here, we are reporting polymeric g-C₃N₄ layers coated with different propositions of erbium oxide nanoparticles, characterized using XPS, UV-Vis-DRS, FT-IR, HR-TEM, FE-SEM, elemental mapping, XRD and surface area techniques and its photocatalytic activities were evaluated under visible light irradiations. The hybrid nanocomposite materials possess better crystalline nature and erbium oxide particles were on the surface of polymeric g-C₃N₄. The surface area and bandgap energy of the polymeric g-C₃N₄-erbium oxide (5 wt%) nanohybrid composite were 99.9 m²/g and 2.52 eV. The photocatalytic activities as prepared nanohybrid composites were assessed for the oxidation of orange G dye molecules in the presence of visible light and were highly active in a broader range of pH with the presence of various inorganic anions. The rate of photocatalytic oxidation of dye molecules varied from 4.79 × 10^-4 to 1.77 × 10^-4 min^-1 for the initial concentration of 5 to 20 ppm and retained its activities above 95% up to three cycles of reusability. Hence, the organic-inorganic novel catalytic nanohybrid composite may find more comprehensive applications in the area of environmental and energy applications.

Charge transport and heavy metal removal efficacy of graphitic carbon nitride doped with CeO2

Doping of graphitic carbon nitride (g-C₃N₄) with semiconductors prevents electron-hole recombination and enhances adsorption capacity. This work investigates the synthesis of a water remediation material using g-C₃N₄ doped with CeO₂ using two different techniques. The chemical structures of the doped g-C₃N₄ samples were confirmed using FTIR, XRD, XPS and their morphology was studied using SEM-EDX. Charge transport through the doped materials was illustrated by a comprehensive dielectric study using broadband spectroscopy. The ability of doped g-C₃N₄ to adsorb heavy metals was investigated thoroughly in the light of applying different parameters such as temperature, pH, time, and concentration. The results showed that the mode of doping of g-C₃N₄ by CeO₂ strongly affected its adsorption capacity. However, g-C₃N₄ doped with CeO₂ using the first mode adsorbed 998.4 mg g^-1 in case of Pb²⁺ and 448 for Cd²⁺. Kinetic study revealed that the adsorption process obeyed PSORE as its q ^exp _e is close to its q ^cal _e and the rate-controlling step involved coordination among the synthetic materials and the heavy metal ions. The recovery of Pb²⁺ and Cd²⁺ ions from various sorbents was investigated by utilizing different molar concentrations of HNO₃ and indicated no significant change in the sorption capability after three different runs. This study has demonstrated an efficient method to obtain a highly efficient adsorbent for removing heavy metals from waste water.

Visible light active hybrid silver decorated g-C3N4-CeO2 nanocomposite for ultrafast photocatalytic activity and toxicity evaluation

Development of hybrid graphitic carbon nitride (GCN) nanocomposite is an emerging research area in wastewater treatment. Herein, hybrid visible light active photocatalyst of silver decorated polymeric graphitic carbon nitride and (Ag-GCN) with cerium oxide (CeO₂) nanocomposite was prepared and characterized in detail. The Ag-GCN/CeO₂ photocatalyst has successfully prepared by an electrostatic self-assembly approach. The synthesized Ag-GCN/CeO₂ NCs photocatalysts are characterized by various physio-chemical techniques. Using the Ag-GCN/CeO₂ catalyst, the excellent photodegradation efficiency of Acid yellow-36 (AY-36) and Direct yellow-12 (DY-12) dye solution were achieved 100% within 150 min sun light irradiation. The Ag-GCN/CeO₂ rate constant values of 0.048 and 0.046/min has been determined for AY-36 and DR-12 dyes, respectively. The extraordinary photocatalytic activity is due to incorporation of CeO₂ with Ag-GCN which play a significant role in visible light absorption, superior reactive oxygen generation (ROS) and excellent pollutant catalyst interaction. The toxicity of the photocatalytically degraded AY-36 and DR-12 dyes were measured using the soil nematode Caenorhabditis elegans, a well-established in vivo model in biology, by analyzing survival, physiological functions, intracellular ROS levels, and stress-protective gene expressions.

A Facile and Sustainable Enhancement of Anti-Oxidation Stability of Nafion Membrane

^•OH radicals are the main cause of chemical degradation of Nafion membranes in fuel cell operation. Although the cerium ion (Ce^3+/4+, Ce) is reported as an effective ^•OH radical quencher, its membrane application has critical limitations associated with the reduction of membrane proton conductivity and its leaking. In this study, the Ce-grafted graphitic carbon nitrides (g-C₃N₄) (CNCe) nano-particles are synthesized and embedded in Nafion membranes to prolong the ^•OH radical scavenging effect. The synthesis of CNCe nano-particles is evaluated by X-ray diffraction, energy dispersive X-ray analysis, and transmission electron microscopy. Compared with the pristine and Ce-blended Nafion membranes, the CNCe imbedded ones show tremendous improvement in long-term anti-oxidation stability. While the fluoride emission rates of Nafion are 0.0062 mg·cm⁻²·h⁻¹ at the anode and 0.0034 mg·cm⁻²·h⁻¹ at the cathode, those of Nafion/CNCe membranes are 0.0037 mg·cm⁻²·h⁻¹ at the anode and 0.0023 mg·cm⁻²·h⁻¹ at the cathode. The single cell test for Nafion/CNCe membranes at 80 °C and 50% relative humidity illustrates much better durability than those for Nafion and Nafion/Ce, indicating its superior scavenging effect on ^•OH radicals.

TiO2-CeO2/g-C3N4 S-scheme heterostructure composite for enhanced photo-degradation and hydrogen evolution performance with combined experimental and DFT study

The g-C₃N₄/TiO₂ nanocomposites (NCs) are fabricated by optimization of calcination and subsequent hydrothermal technique decorated with CeO₂ nanoparticles (NPs) to build the g-C₃N₄/TiO₂-CeO₂ hybrid NCs. The chemical and surface characterizations of structural, morphological, elemental composition, optical, photo-degradation, HER performance and the DFT computation has been efficiently analyzed. The g-C₃N₄/TiO₂-CeO₂ composite photocatalysts (PCs) exhibit photocatalytic improved performance (∼97 %) for MB aqueous dye related to pristine g-C₃N₄ and g-C₃N₄/TiO₂ composite PCs. The obtained k value of the g-C₃N₄/TiO₂/CeO₂ heterostructure composite PCs has around 0.0262 min^-1 and 6.1, 2.6 and 1.5 times higher than to g-C₃N₄ (0.0043 min^-1), g-C₃N₄/CeO₂ (0.0099 min^-1) and g-C₃N₄/TiO₂ (0.0180 min^-1) PCs respectively. Likewise, the synergistic probable S-scheme charge separation mechanism based on scavengers' tests and other values, which leads to effective separation of photo-excited (e^--h⁺) pairs, whereas high degradation and more H₂O molecules have photo-reduction to H₂. The H₂ evolution reaction (HER) and the electrochemical impedance spectroscopy (EIS) of the as-obtained samples were explored via electrochemical study. This exertion recommends that the rational strategy and building of g-C₃N₄/TiO₂-CeO₂ nano-heterostructures were beneficial for developing visible-light-driven recyclable PCs for ecological refinement.

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.

Controlled hydrothermal synthesis of BiOxCly/BiOmBrn/g-C3N4 composites exhibiting visible-light photocatalytic activity

The first systematic synthesis of bismuth oxychloride/bismuth oxybromide/graphitic carbon nitride (BiO_xCl_y/BiO_mBr_n/g-C₃N₄) nano-composites used a controlled hydrothermal method. The structure, morphology and characteristic of BiO_xCl_y/BiO_mBr_n/g-C₃N₄ photocatalyst were measured by XRD, UV-vis-DRS, FT-IR, FE-TEM, FE-SEM-EDS, PL, BET, HR-XPS and EPR. Under visible light irradiation, the photodegradation activity was evaluated for the decolorization of crystal violet (CV) and 2-hydroxybenzoic acid (2-HBA) in aqueous solution. The catalytic performance showed that, when using sample BB2C1-4-250-30 wt% g-C₃N₄ composite as a photocatalyst, the best reaction-rate-constant (k) was 0.071 h^-1. It was 1.5 times higher than the k value of BB2C1-4-250 as a photocatalyst. From the scavenging effect of various scavengers, the results of EPR showed that reactive OH was the main scavenger, while O₂^-, h⁺ and ¹O₂ were the second scavenger in CV degradation. In this study, a possible photodegradation mechanism was proposed and discussed. In this work, our method of BiO_xCl_y/BiO_mBr_n/g-C₃N₄ preparation could be used for future mass production and the BiO_xCl_y/BiO_mBr_n/g-C₃N₄ composite materials could be applied to the environmental pollution control in future.

An Interface Optimization Strategy for g-C3N4-Based S-Scheme Heterojunction Photocatalysts

Graphitic carbon nitride (CN) has attracted much attention in photocatalytic fields due to its unique electronic band structure. However, the rapid recombination of photogenerated carriers severely inhibits its catalytic activity. The heterojunction structure has been widely confirmed to significantly improve the photocatalytic activity of CN through the formed interface structure. However, researchers often give attention to the band matching and conductivity of the cocatalyst, while the importance of the interface as a migration channel for photogenerated carriers is often overlooked. In this work, we adopt the strategy of morphology engineering to regulate the morphology of the CN photoactive component so as to achieve the interface optimization of the traditional heterojunction structure. The photocatalytic degradation experiment of rhodamine B shows that compared with the traditional CeO₂@CN heterojunction structure, the photocatalytic activity of the interface-optimized CeO₂/CN is increased by more than 20%. The following points could be used to explain the improvement of photocatalytic activity: (I) the formed S-scheme heterojunction structure, which inhibits the recombination of useful electrons and holes but expedites the recombination of relatively useless electrons and holes, (II) the increased interface area, which provides more carrier migration channels, and (III) the reduced interface contact resistance, which facilitates the separation and migration of photogenerated carriers. Furthermore, the interface optimization of the traditional Al₂O₃@CN and Fe₂O₃@CN heterojunction structures also achieved consistent results. This shows that the strategy in this work is a universal method for interface optimization, which provides potential alternative for further improving the catalytic activity of other heterojunction composites.

A CeO2 Semiconductor as a Photocatalytic and Photoelectrocatalytic Material for the Remediation of Pollutants in Industrial Wastewater: A Review

The direct discharge of industrial wastewater into the environment results in serious contamination. Photocatalytic treatment with the application of sunlight and its enhancement by coupling with electrocatalytic degradation offers an inexpensive and green technology enabling the total removal of refractory pollutants such as surfactants, pharmaceuticals, pesticides, textile dyes, and heavy metals, from industrial wastewater. Among metal oxide—semiconductors, cerium dioxide (CeO2) is one of the photocatalysts most commonly applied in pollutant degradation. CeO2 exhibits promising photocatalytic activity. Nonetheless, the position of conduction bands (CB) and valence bands (VB) in CeO2 limits its application as an efficient photocatalyst utilizing solar energy. Its photocatalytic activity in wastewater treatment can be improved by various modification techniques, including changes in morphology, doping with metal cation dopants and non-metal dopants, coupling with other semiconductors, and combining it with carbon supporting materials. This paper presents a general overview of CeO2 application as a single or composite photocatalyst in the treatment of various pollutants. The photocatalytic characteristics of CeO2 and its composites are described. The main photocatalytic reactions with the participation of CeO2 under UV and VIS irradiation are presented. This review summarizes the existing knowledge, with a particular focus on the main experimental conditions employed in the photocatalytic and photoelectrocatalytic degradation of various pollutants with the application of CeO2 as a single and composite photocatalyst.

Emerging Chemical Functionalization of g-C3N4: Covalent/Noncovalent Modifications and Applications

Atomically 2D thin-layered structures, such as graphene nanosheets, graphitic carbon nitride nanosheets (g-C₃N₄), hexagonal boron nitride, and transition metal dichalcogenides are emerging as fascinating materials for a good array of domains owing to their rare physicochemical characteristics. In particular, graphitic carbon nitride has turned into a hot subject in the scientific community due to numerous qualities such as simple preparation, electrochemical properties, high adsorption capacity, good photochemical properties, thermal stability, and acid-alkali chemical resistance, etc. Basically, g-C₃N₄ is considered as a polymeric material consisting of N and C atoms forming a tri-s-triazine network connected by planar amino groups. In comparison with most C-based materials, g-C₃N₄ possesses electron-rich characteristics, basic moieties, and hydrogen-bonding groups owing to the presence of hydrogen and nitrogen atoms; therefore, it is taken into account as an interesting nominee to further complement carbon in applications of functional materials. Nevertheless, g-C₃N₄ has some intrinsic limitations and drawbacks mainly related to a relatively poor specific surface area, rapid charge recombination, a limited light absorption range, and a poor dispersibility in both aqueous and organic mediums. To overcome these shortcomings, numerous chemical modification approaches have been conducted with the aim of expanding the range of application of g-C₃N₄ and enhancing its properties. In the current review, the comprehensive survey is conducted on g-C₃N₄ chemical functionalization strategies including covalent and noncovalent approaches. Covalent approaches consist of establishing covalent linkage between the g-C₃N₄ structure and the chemical modifier such as oxidation/carboxylation, amidation, polymer grafting, etc., whereas the noncovalent approaches mainly consist of physical bonding and intermolecular interaction such as van der Waals interactions, electrostatic interactions, π-π interactions, and so on. Furthermore, the preparation, characterization, and diverse applications of functionalized g-C₃N₄ in various domains are described and recapped. We believe that this work will inspire scientists and readers to conduct research with the aim of exploring other functionalization strategies for this material in numerous applications.

Synthesis and Characterization of Efficient ZnO/g-C3N4 Nanocomposites Photocatalyst for Photocatalytic Degradation of Methylene Blue

We examine the photocatalytic activity (PCA) of ZnO/graphitic carbon nitride g-C3N4 (g-CN) composite material for methylene blue (MB) degradation under visible-light irradiation (VLI). The polymeric g-CN materials were fabricated by the pyrolysis of urea and thiourea. More importantly, ZnO/g-CN nanostructured composites were fabricated by adding the different mounts (60, 65, 70, and 75 wt.%) of g-CN into ZnO via the simple hydrothermal process. Among fabricated composites, the 75% ZnO/g-CN nanocomposites displayed a superior PCA for MB degradation, which were ~three-fold an enhancement over the pure ZnO nanoparticles. The fabricated materials have been evaluated by X-ray diffraction (XRD), UV-Vis, Fourier transform infrared (FT-IR) spectroscopy, and electron microscopy. More importantly, the photodegradation of MB could get 98% in ZnO/g-CN could be credited to efficient separation of photo-induced charge carriers between ZnO and g-CN. Also, the recycling efficiency of the as-prepared composites was studied for multiple cycles, which shows that the photocatalysts are stable and suitable to carry out photocatalytic degradation in the logistic mode. Additionally, the probable photocatalytic mechanism has also discussed. The synthetic procedure of ZnO/g-CN based materials can be used in numerous fields such as environmental and in energy storage applications.

Preparation of pyramidal SnO/CeO2 nano-heterojunctions with enhanced photocatalytic activity for degradation of tetracycline

Pyramidal SnO/CeO₂ nano-heterojunction photocatalysts were successfully synthesized via a facile hydrothermal method. The structural characterization was investigated by using common characterization tools. The content of SnO affected the morphology and photocatalytic performance of the SnO/CeO₂ nano-heterojunctions. With the increase of the SnO content, the morphology of the samples changed from a spherical structure to a pyramidal structure. The photocurrent of the SnO/CeO₂ (1:6) sample was about 36 times that of pure CeO₂. With SnO/CeO₂ (1:6) as the photocatalyst, the degradation rate of tetracycline (TC) was 99% within 140 min under visible light and after five cyclic tests the photocatalytic efficiency of TC remained at 98%, which suggests that the SnO/CeO₂ (1:6) nano-heterojunction had a high photocatalytic efficiency and stable photocatalytic performance. These results indicate that SnO/CeO₂ (1:6) nano-heterojunction possesses broad prospects for industrial application.

Enhanced reduction and oxidation capability over the CeO2/g-C3N4 hybrid through surface carboxylation: performance and mechanism

The charge separation efficiency of the CeO₂/g-C₃N₄ heterojunction was greatly enhanced through surface carboxylation of the g-C₃N₄ substrate.

Nanotechnology in remediation of water contaminated by poly- and perfluoroalkyl substances: A review

This article gives an overview of nanotechnologies applied in remediation of water contaminated by poly- and perfluoroalkyl substances (PFASs). The use of engineered nanomaterials (ENMs) in physical sorption and photochemical reactions offers a promising solution in PFAS removal because of the high surface area and the associated high reactivities of the ENMs. Modification of carbon nanotubes (CNTs) (e.g., oxidation, applying electrochemical assistance) significantly improves their adsorption rate and capacity for PFASs removal and opens a new door for use of CNTs in environmental remediation. Modified nanosized iron oxides with high adsorption capacity and magnetic property have also been demonstrated to be ideal sorbents for PFASs with great recyclability and thus provide an excellent alternative for PFAS removal under various conditions. Literature shows that PFOA, which is one of the most common PFASs detected at contaminated sites, can be effectively decomposed in the presence of either TiO₂-based, Ga₂O₃-based, or In₂O₃-based nano-photocatalysts under UV irradiation. The decomposition abilities and mechanisms of different nano-photocatalysts are reviewed and compared in this paper. Particularly, the nanosized In₂O₃ photocatalysts have the best potential in PFOA decomposition and the decomposition performance is closely related to the specific surface area and the amount of photogenerated holes on the surfaces of In₂O₃ nanostructures. In addition to detailed review of the published studies, future prospects of using nanotechnology for PFAS remediation are also discussed in this article.

Amplified photoelectrochemical immunoassay for the tumor marker carbohydrate antigen 724 based on dye sensitization of the semiconductor composite C3N4-MoS2

The authors describe an amplified photoelectrochemical immunoassay for the tumor marker carbohydrate antigen 724 (CA724). The method employs a C₃N₄-MoS₂ semiconductor as the photoelectric conversion layer. The nanocomposite was characterized by transmission electron microscopy, Fourier transform infrared spectroscopy, X-ray powder diffraction, and UV-vis diffuse reflectometry. The dye eosin Y was encapsulated into CaCO₃ nanospheres which then were used as labels for antibody against CA724. In addition, Fe₃O₄ nanospheres were employed as magnetic platform for constructing photoelectrochemical sandwich immunoassay. The CaCO₃ nanospheres can be dissolved with aid of ethylene diamine tetraacetic acid (EDTA) and the carried eosin Y in CaCO₃ is released. The released dyes sensitizes the C₃N₄-MoS₂ semiconductor, which induces photocurrent amplification. Under optimal conditions and at a typical working voltage of 0 V (vs. SCE), the photocurrent increases linearly in the range of 0.05 mU mL^-1 to 500 mU mL^-1 of CA724, with a 0.02 mU mL^-1 detection limit. Graphical abstract The C₃N₄-MoS₂ complex, with high efficiency of electron transport, was synthesized to construct a photoelectrochemical analytical platform. A sandwich-type immunoassay was established on the surface of magnetic beads. Carbohydrate antigen 724 in sample was detected sensitively by using sensitization of released eosin Y as signal amplifiery.