Oxygen Vacancy-Mediated Z-Scheme Charge Transfer in a 2D/1D B-Doped g-C3N4/rGO/TiO2 Heterojunction Visible Light-Driven Photocatalyst for Simultaneous/Efficient Oxygen Reduction Reaction and Alcohol Oxidation.

Hydrogen peroxide (H2O2) is a powerful oxidant that directly or indirectly oxidizes many organic and inorganic contaminants. The photocatalytic generation of H2O2 is achieved by using a semiconductor photocatalyst in the presence of alcohol as a proton source. Herein, we have synthesized oxygen vacancy (Ov)-mediated TiO2/B-doped g-C3N4/rGO (TBCN@rGO) ternary heterostructures by a simple hydrothermal technique. Several characterization techniques were employed to explore the existence of oxygen vacancies in the crystal structure and investigate their impact on the optoelectronic properties of the catalyst. Oxygen vacancies offered additional sites for adsorbing molecular oxygen, activating alcohols, and facilitating electron migration from TBCN@rGO to the surface-adsorbed O2. The defect creation (oxygen vacancy) and Z-scheme mechanistic pathways create a suitable platform for generating H2O2 by two-electron reduction processes. The optimized catalyst showed the highest photocatalytic H2O2 evolution rate of 172 µmol/h, which is 1.9 and 2.5 times greater than that of TBCN and BCN, respectively. The photocatalytic oxidation of various lignocellulose-derived alcohols (such as furfural alcohol and vanillyl alcohol) and benzyl alcohol was also achieved. Photocatalytic activity data, physicochemical and optoelectronic features, and trapping experiments were conducted to elucidate the structure-activity relationships. The TBCN@rGO acts as a multifunctional Z-scheme photocatalyst having an oxygen vacancy, modulates surface acidity-basicity required for the adsorption and activation of the reactant molecules, and displays excellent photocatalytic performance due to the formation of a large number of active surface sites, increased electrical conductivity, improved charge transfer properties, outstanding photostability, and reusability. The present study establishes a unique strategy for improving H2O2 generation and alcohol oxidation activity and also provides insights into the significance of a surface vacancy in the semiconductor photocatalyst.

Challenges and prospects in the selective photoreduction of CO2 to C1 and C2 products with nanostructured materials: a review.

Solar fuel generation through CO2 hydrogenation is the ultimate strategy to produce sustainable energy sources and alleviate global warming. The photocatalytic CO2 conversion process resembles natural photosynthesis, which regulates the ecological systems of the earth. Currently, most of the work in this field has been focused on boosting efficiency rather than controlling the distribution of products. The structural architecture of the semiconductor photocatalyst, CO2 photoreduction process, product analysis, and elucidating the CO2 photoreduction mechanism are the key features of the photoreduction of CO2 to generate C1 and C2 based hydrocarbon fuels. The selectivity of C1 and C2 products during the photocatalytic CO2 reduction have been ameliorated by suitable photocatalyst design, co-catalyst, defect states, and the impacts of the surface polarisation state, etc. Monitoring product selectivity allows the establishment of an appropriate strategy to generate a more reduced state of a hydrocarbon, such as CH4 or higher carbon (C2) products. This article concentrates on studies that demonstrate the production of C1 and C2 products during CO2 photoreduction using H2O or H2 as an electron and proton source. Finally, it highlights unresolved difficulties in achieving high selectivity and photoconversion efficiency of CO2 in C1 and C2 products over various nanostructured materials.

Exfoliated Boron Nitride (e-BN) Tailored Exfoliated Graphitic Carbon Nitride (e-CN): An Improved Visible Light Mediated Photocatalytic Approach towards TCH Degradation and H2 Evolution.

A series of 2D/2D exfoliated boron nitride/exfoliated g-C3N4 nanocomposites denoted as e-BN/e-CN have been successfully prepared using a simple in situ technique. The successful deposition of e-BN on e-CN was confirmed from high-resolution transmission electron microscopy analysis. According to electrochemical measurements, 1.5 wt % e-BN/e-CN nanocomposites showed 1.5 times more photocurrent than e-CN, which indicates the successful formation of an e-BN/e-CN heterostructure. The photocatalytic activities of the e-CN and e-BN/e-CN composites were investigated through photocatalytic tetracycline hydrochloride (TCH) degradation and H2 evolution under visible light illumination. The 1.5 wt % e-BN/e-CN composite demonstrated the highest photocatalytic activities, which are about 21 and 1.5 fold greater than e-CN towards H2 generation with an apparent conversion efficiency of 2.34% and TCH degradation, respectively. The improved photocatalytic activities of e-BN/e-CN photocatalysts were ascribed to the augmented light-harvesting ability and enhanced separation efficiency of charge carriers. Lower photoluminescence intensity and a smaller arc value in the impedance spectra again proved the reduced recombination of the e--h+ pairs in the e-BN/e-CN nanocomposites. Trapping experiments show that •O2-, h+, and •OH radicals are the predominant reactive species that accelerated the photocatalytic activities of e-BN/e-CN composites. This study opens up a new window towards the fabrication of such 2D/2D nanocomposites in the field of photocatalysis.

Prominence of Cu in a plasmonic Cu-Ag alloy decorated SiO2@S-doped C3N4 core-shell nanostructured photocatalyst towards enhanced visible light activity.

A series of Cu-Ag bimetal alloys decorated on SiO2 and the fabrication of few-layer S-doped graphitic carbon nitride (SC) warped over it to form a core-shell nanostructured morphology have been demonstrated and well characterized through various physiochemical techniques. HRTEM data confirmed the formation of a compact nanojunction between the SiO2 and SC, where Cu-Ag is embedded uniformly with an average particle size of 1.3 nm. The Ag : Cu (1 : 3) between SiO2 and SC produces 1730 µmol h-1 g-1 of H2 under visible light illumination. Moreover, 6.2-fold current enhancement in the case of Ag : Cu (1 : 3) as compared to the Ag-loaded core-shell nanostructured photocatalyst indicates higher electron-hole-pair separation. The excellent activity was due to the synergistic alloying and plasmonic effect of Ag and Cu. DFT studies reveal that the Cu atom in the Cu-Ag bimetal alloy plays a pivotal role in the generation of H2, and the reaction proceeds via a 4-membered transition state. The mechanistic insight proceeds from the generation of hot electrons due to the LSPR effect and their transfer to the SC layer via a compact nanojunction.

Novel Magnetic Retrievable Visible-Light-Driven Ternary Fe3O4@NiFe2O4/Phosphorus-Doped g-C3N4 Nanocomposite Photocatalyst with Significantly Enhanced Activity through a Double-Z-Scheme System.

Nickel ferrite (NiFe2O4) and magnetite (Fe3O4) are established earth-abundant materials and get tremendous attention because of magnetic and high photocatalytic activity. First we fabricated novel Fe3O4@20 wt % NiFe2O4/phosphorus-doped g-C3N4 (M@NFOPCN) using a convenient simple coprecipitation method followed by calcination at 400 °C. Then M@NFOPCN composites were prepared by the in situ growth of Fe3O4 nanorods and cubes on the surfaces of a porous agglomerated NFOPCN nanostructure, varying the weight percentage of Fe3O4. A series of characterizations like X-ray diffraction, UV-vis diffuse-reflectance spectroscopy, photoluminescence, Fourier transform infrared, thermogravimetric analysis-differential thermal analysis, vibrating-sample magnetometry, scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy techniques confirm that changing weight percentage of M can constructively control the textural characteristics, internal strain, size of the crystals, and other aspects meant for photocatalytic activity. When M was coupled with NFOPCN, magnetic loss was lowered and also an appreciable saturation magnetization (Ms) was obtained. 40 wt % M@NFOPCN showed admirable photostability and was capable of evolving 924 µmol h-1 H2 when irradiated under visible light. The percentage of degradation for ciprofloxacin (CIP) by this ternary nanocomposite was almost 2-fold greater than those of the pure M and NFOPCN photocatalysts. A plausible photocatalytic mechanism for the degradation of CIP antibiotic was established. Hence, this study presents a reusable, low-cost, noble-metal-free, environmentally friendly, fast, and highly efficient 40 wt % M@NFOPCN photocatalyst, achieving 90% degradation of CIP antibiotic under visible light. The double-Z scheme triggers charge separation and migration, enhances visible-light harvesting, and helps in internal electric-field creation, thus headed toward dramatic augmentation of the photocatalytic activity.

Bandgap engineering via boron and sulphur doped carbon modified anatase TiO2: a visible light stimulated photocatalyst for photo-fixation of N2 and TCH degradation.

The present research reports the synthesis of two-dimensional (2D) sheet/flake-like nanostructures of crystalline carbon modified TiO2 (CT), B-TiO2 (B-CT), and S-TiO2 (S-CT) using a facile one-pot synthesis method. The crystallinity and phase purity (anatase) of the prepared nano-photocatalyst were characterised using X-ray diffraction, selected area electron diffraction (SAED) and high-resolution transmission electron microscopy (HRTEM) analysis. Furthermore, the morphological details and elemental content of the sample were studied via scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS), respectively. Additionally, the optoelectronic features of all of the prepared specimens were measured via UV-vis diffuse reflectance spectroscopy (DRS), photoluminescence (PL), impedance and Mott-Schottky studies. After successful characterisation, their photocatalytic performance was tested towards dinitrogen photo-fixation and tetracycline hydrochloride (TCH) degradation under visible light illumination. Moreover, the effective charge separation and greater availability of the active surface area led to the robust photocatalytic activity of the fabricated B-CT compared to the CT and S-CT samples, which correlates well with the PL, impedance and surface area analysis. B-CT displays the highest photocatalytic activity, i.e. 32.38 µmol L-1 (conversion efficiency = 0.076%) of ammonia production, and 95% tetracycline hydrochloride (10 ppm) degradation. Here, we have effectively designed a novel and productive pathway towards the enhancement of the photocatalytic performance of visible photon active TiO2-based materials for energy and environmental sustainability.

Enhanced photocatalytic activities of polypyrrole sensitized zinc ferrite/graphitic carbon nitride n-n heterojunction towards ciprofloxacin degradation, hydrogen evolution and antibacterial studies.

Fusion of heterogeneous photocatalysts with conducting polymers has paid a rising stratagem in the field of photocatalysis owing to its biocompatibility and environment friendliness. In this work a series of polypyrrole (PPY) sensitized zinc ferrite/graphitic carbon nitride (ZFCN) n-n heterojunction (ZFCN@10PPY, ZFCN@20PPY, and ZFCN@30PPY) nanocomposite were fabricated by in-situ polymerization method. Due to low band gap of polypyrrole, it behaves as a photo-sensitizer, supplies surplus numbers of electrons to ZnFe2O4/g-C3N4 n-n heterojunction and improves the photocatalytic performance. The fabricated ZFCN@20PPY exhibits highest photocatalytic activity in comparison to others nanocomposites. The superior photocatalytic performance of ZFCN@20PPY was ascribed to the tunable band structure, synergistic effect of broad absorption upto NIR region, delayed electron-hole recombination and efficient charge transfer across the junction interface which has been well confirmed from UV-Vis DRS, PL and EIS measurement. Further the photocatalytic activity of ZFCN@20PPY was supported by both n-type and p-type photocurrent density i.e. 2.4 and 3.9 mA/cm2 respectively. ZFCN@20PPY shows good photocatalytic performance towards ciprofloxacin degradation (92%) and generation of hydrogen energy (567 µmol). Along with pollutant degradation and energy production ZFCN@20PPY also shows its potential towards antibacterial activities against human pathogenic bacteria like Escherichia coli. These newly designed polymer sensitized n-n heterojunction may offer a promising strategy for maximum light absorption and be authoritative in meeting the environmental claims in the future.

Constructive Interfacial Charge Carrier Separation of a p-CaFe2O4@n-ZnFe2O4 Heterojunction Architect Photocatalyst toward Photodegradation of Antibiotics.

Charge dynamics across the interfacial junction of p-n heterostructures leading to effective charge separation along with notable photodurability are essential preconditions to achieve high photocatalytic activity. The p-CaFe2O4@n-ZnFe2O4 (CFO@ZFO) heterojunction has been successfully synthesized by a simple solution combustion method followed by the ultrasonication technique. XRD and HRTEM studies confirmed the effective interaction and formation of the CFO@ZFO heterojunction. The loading of CFO over ZFO selectively enhanced the intensity of the (111) plane of active ZFO, leading to greater crystallinity and a suitable heterojunction which triggers the photocatalytic reaction. The result shows that a 40% loading of CFO on ZFO makes it the flagship photocatalyst. The impedance and PL spectra of 40%CFO@ZFO confirmed the low electron-hole recombination in comparison to the neat materials. Bode phase analysis showed that the lifetime exciton in 40%CFO@ZFO is 1.35 times superior to that of pure ZFO. The heterostructure results in enhancement of the photocurrent in the anodic direction, i.e. 6.6 mA/cm2, which is nearly 2 times greater that of the neat materials. The 40%CFO@ZFO shows the best activity toward degradation of 20 ppm tetracycline and ciprofloxacin, i.e. 89.5% and 78%, respectively, in 1 h. The efficient charge separation at the interface, low charge transfer resistance, formation of heterostructures, and high value of synergy factor are collectively responsible for the best activity in 40%CFO@ZFO.

Facile synthesis of ZnFe2O4@RGO nanocomposites towards photocatalytic ciprofloxacin degradation and H2 energy production.

The production of Hydrogen energy through the splitting of water is a promising pathway for clean environment and sustainability. Herein we have synthesized a series of ZnFe2O4 (ZFO)@Reduced Graphene Oxide (RGO) nanocomposites by hydrothermal followed by calcination method and studied its application towards hydrogen energy production and ciprofloxacin degradation. Powder X-ray diffraction (XRD) study and X-ray photoelectron spectroscopy (XPS) analysis indicate the good crystallinity and suitable chemical environment for the photocatalytic process. Among all the samples, ZFO@3%RGO showed 73.4% of CIP degradation under solar irradiation of 1 h, which is 1.67 times higher than that of pure ZFO nanoparticles. CIP degradation process follows first order kinetics with a good rate constant of 0.021 min-1 which is 2.3 times greater than ZFO. The photocatalyst ZFO@3%RGO illustrated maximum H2 energy production i.e. 410.32 µmol/h, which is 1.35 times more than that of neat ZFO nanoparticles. ZFO@3%RGO demonstrates the highest photocurrent density of 0.6 mA/cm2 under light illuminations, which is 250 times superior to that of the pristine photocatalyst. Bode phase analysis confirmed that ZFO@RGO shows 13 times higher charge separation efficiency in comparison to neat ZFO. The best photocatalytic activity of ZFO@3%RGO nanocomposite is due to its high light absorption capacity, low photogenerated exciton recombination, high electron-hole separation, and high photocurrent density.

Synergistic ZnFe2O4-carbon allotropes nanocomposite photocatalyst for norfloxacin degradation and Cr (VI) reduction.

Development of highly efficient robust catalyst for pollutant abetment still remains an ongoing scientific challenge in the field of visible light driven photocatalysis. In this work a series of ZnFe2O4 (ZFO)/carbon derivatives (ZFO@CNT, ZFO@GO, ZFO@Fullerene) nanocomposite were fabricated by one-pot hydrothermal method followed by calcination. The detail anatomical featured such as crystal geometry, morphology, elemental composition, light absorption performance, electron-hole recombination properties and photocurrent density were characterized by XRD, SEM, HRTEM, XPS, UV-Vis DRS, PL and electrochemical analysis respectively. The photocatalytic performances of ZFO@carbon nanocomposites were studied for the degradation of antibiotics (Norfloxacin) and hexavalent Chromium under open sun light illumination and the obtained results suggested that loading of carbon derivatives of ZFO nanoparticles enhance the visible light absorption capacity and excitation separation efficiency. Among the fabricated composites, ZFO@CNT exhibits the highest activity in comparison to other nanocomposites. The highest activity of ZFO@CNT is due to low photoexcited electron-hole recombination and high charge transfer properties of ZFO@CNT as confirmed via PL and impedance measurement. Further, the fabricated ZFO@CNT nanocomposite exhibited highest photocurrent density i.e. 2.25 mA/cm2 which was 225 times higher than that of neat ZFO. The optimal photocatalytic efficiency was shown by ZFO@CNT i.e. 91.36% degradation of 50 ppm norfloxacin and 82% reduction of 10 ppm Cr (VI) in 90 min and 60 min respectively under solar light irradiation.

HPW-Anchored UiO-66 Metal-Organic Framework: A Promising Photocatalyst Effective toward Tetracycline Hydrochloride Degradation and H2 Evolution via Z-Scheme Charge Dynamics.

The abolition of environmental pollutants and production of hydrogen (H2) from water using a heterogeneous photocatalyst is a demanding science of the current scenario to solve the increasing environmental pollution and worldwide energy catastrophe in modern life. To validate this purpose, the design of low-cost and durable semiconductor-based photocatalysts with great light absorption capacity becomes the most challenging issue for researchers. Regarding this, herein the phosphotungstic acid (HPW)-anchored Zr6O4(OH)4(BDC)6 (UiO-66) metal-organic framework (MOF), i.e., HPW@UiO-66, has been prepared by a hydrothermal method and is efficient, stable, and capable of harvesting solar energy toward the degradation of tetracycline hydrochloride (TCH) and H2 production in the presence of a sacrificial donor. The ionic interaction between HPW and UiO-66 plays a key role toward the photostability and charge-transfer mechanism of the composite and is well characterized with X-ray diffraction, UV diffuse-reflectance spectroscopy, Fourier transform infrared, and X-ray photoelectron spectroscopy. A total of 30 wt % HPW@UiO-66 shows a maximum degradation of about 87.24% of a 20 ppm TCH solution in 60 min of solar-light irradiation and about 353.89 µmol/h of H2 production. The conduction- and valence-band potentials are well characterized with Mott-Schottky measurement and a delay charge recombination process through electrochemical impedance spectroscopy. The proposed mediator-free Z-scheme-oriented electron-hole migration route is well supported by photoluminescence, and the scavenger test well explains the better charge-carrier separation and high catalytic performance of the prepared composite. This research will bestow an advantageous blueprint to fabricate novel and challenging photocatalysts toward the photocatalytic treatment of environmental pollutants and H2 evolution.

Facile construction of a novel NiFe2O4@P-doped g-C3N4 nanocomposite with enhanced visible-light-driven photocatalytic activity.

Construction of a Z-scheme-based photocatalyst, i.e., NiFe2O4@P-g-C3N4 nanocomposite, was successfully fabricated by coupling phosphorus-doped g-C3N4 with spinel structure NiFe2O4. The structural, morphological, and spectroscopic data of the as-synthesized photocatalyst was successfully characterized through XRD, FTIR, SEM, TEM, UV-Vis DRS, PL, and XPS techniques. It was found that NiFe2O4@P-g-C3N4 had an increased light-absorption capacity, high exciton separation, low photogenerated electron-hole recombination, and showed better photocatalytic activity toward phenol oxidation and hydrogen energy production than the neat materials. Photocatalytic phenol oxidation by 20 wt% NFO@P-CN was also superior and could achieve a 96% conversion, which was 2 and 3 times higher than that by P-CN and NFO, respectively. The 20 wt% NFO@P-CN showed excellent photostability and was able to evolve 904 µmol h-1 H2 under visible-light irradiation. The enhanced photocatalytic activity of NiFe2O4@P-g-C3N4 was in good agreement with the photocurrent results. The synergistic effect between P-CN and NFO could accelerate photogenerated charge separation and, moreover, the distinctive magnetism of NiFe2O4@P-g-C3N4 aided the collection and recycling of the photocatalyst.

Facile synthesis of ZnFe2O4 photocatalysts for decolourization of organic dyes under solar irradiation.

ZnFe2O4 was fabricated by a simple solution-combustion method. The structural, optical and electronic properties are investigated by XRD, TEM, FESEM, UV-vis DRS, PL, FTIR and photocurrent measurements. The photocatalytic activity of the prepared material is studied with regard to the degradation of rhodamine B (Rh B) and Congo red under solar irradiation. The kinetic study showed that the material exhibits zeroth and first order reaction kinetics for the degradation of Rh B and Congo red, respectively. The photocatalytic behaviour of ZnFe2O4 was systematically studied as a function of the activation temperature. ZnFe2O4 prepared at 500 °C showed the highest activity in degrading Rh B and Congo red. The highest activity of ZnFe2O4-500 °C correlates well with the lowest PL intensity, highest photocurrent and lowest particle size.