SrTiO3@NiFe LDH core–shell composites for photocatalytic CO2 conversion

A series of core@shell SrTiO₃@NiFe LDH composites (STONFs) were synthesized and their photocatalytic CO₂ reduction performance was studied. The photocatalyst STONF 2 exhibited enhanced CO₂ reduction performance with CO yield of 7.9 μmol g⁻¹ h⁻¹. The yield was 25.7 times and 8.8 times higher than that of NiFe LDH and SrTiO₃ respectively, and also higher than most LDH based photocatalysts. Compared with two individual components, STONFs exhibited their combined merits of widened absorption spectrum, higher transportation efficiency and alleviated recombination of e⁻/h⁺ pairs. In addition, there were fewer oxygen vacancies in STONF 2 than as-prepared SrTiO₃. Lower oxygen vacancies concentration would increase the opportunity of direct bonding between interface atoms of two components and successively increase the electron transportation and separation. These factors synergistically contributed to enhanced photocatalytic performance. This work will provide new insight for designing complementary multi-component photocatalysis systems.

A series of core@shell SrTiO₃@NiFe LDH composites (STONFs) were synthesized and their photocatalytic CO₂ reduction performance was studied.     

Hydrogen peroxide-assisted synthesis of oxygen-doped carbon nitride nanorods for enhanced photocatalytic hydrogen evolution

Polymer-derived carbon nitrides based photocatalysts are very promising for solar water splitting, CO₂ reduction and environmental remediation. However, these photocatalysts still suffer from low visible light utilization efficiency, rapid recombination of photogenerated charge carriers and slow transfer kinetics. Herein, we report a hydrogen peroxide-assisted hydrothermal strategy to synthesize one-dimensional oxygen-doped carbon nitrides (OCN) for photocatalytic hydrogen evolution. A possible self-assembly mechanism is discussed. Experimental results and theoretical calculations indicate that the as-synthesized one-dimensional OCN possess narrowed band gap energy and optimized band structure, which may allow more effective visible-light harvesting and facilitate photogenerated electron–hole pair separation and transfer. As a result, the photocatalytic hydrogen evolution rates improve from 10.4 μmol h⁻¹ to 74.0 μmol h⁻¹ under visible light (λ > 400 nm), which is among the best of the reported CN-based photocatalysts for visible-light-driven hydrogen evolution. This study provides a new avenue toward the development of highly efficient carbon nitrides based photocatalysts for photocatalytic applications.

One-dimensional oxygen-doped carbon nitride nanorods synthesized via a hydrogen peroxide-assisted process exhibit enhanced hydrogen evolution under visible light.     

Fast photocatalytic degradation of dyes using low-power laser-fabricated Cu2O–Cu nanocomposites

In this study, we report a simple method to controllably synthesize Cu₂O–Cu nanocomposites by using a low-power CO₂ laser, and application of these nanomaterials for photocatalytic degradation of methylene blue (MB). Our experiments demonstrate that efficient tailoring of the Cu₂O–Cu nanocomposites can be realized by accurate control and optimization of the ambient parameters, such as laser energy and NaOH concentration. Compared to hydrothermally fabricated Cu₂O–Cu catalysts, the laser-reduced composites exhibit better visible-light photocatalytic activity for MB degradation, which could be attributed to the formation of special catalytically active structures on the nanocomposite surface. Under the conditions of 10 mA laser irradiation and 5 M NaOH addition, the fabricated Cu₂O–Cu composites had the highest catalytic activity. The degradation rate of MB is 90.10% after visible-light irradiation for 50 min under the optimum conditions. The as-synthesized Cu₂O–Cu composites showed selective dye degradation, and exhibit relatively higher photocatalytic efficiency for positively charged dyes. This work could lead to facile synthesis of high-performance photocatalysts for fast removal of environmentally hazardous dyes from aqueous solution.

Facile synthesis of Cu₂O–Cu nanocomposites by using a low-power CO₂ laser was realized, and the fabricated nanomaterials showed excellent photocatalytic activity for the degradation of various dyes.     

Nanostructural catalyst: metallophthalocyanine and carbon nano-onion with enhanced visible-light photocatalytic activity towards organic pollutants

Metallophthalocyanine (MPc) and carbon nano-onion (CNO) derivatives were synthesized and characterized by using ultraviolet-visible spectroscopy, infrared and Raman spectroscopy, scanning electron microscopy with energy-dispersive X-ray spectroscopy and X-ray powder diffraction. The unmodified CNOs and MPc–CNO derivatives were used as photocatalysts for rhodamine B (RhB) degradation under visible-light irradiation. The photocatalytic studies revealed that the MPc–CNO nanostructural materials simultaneously exhibited a high absorption capacity and an excellent visible-light-driven photocatalytic activity towards RhB. These nanostructures possess great potential for use as active photocatalysts for organic pollutant degradation.

The photocatalytic studies revealed that metallophthalocyanine–carbon nano-onion nanostructural materials simultaneously exhibited a high absorption capacity and an excellent visible-light-driven photocatalytic activity towards rhodamine B.     

Preparation and visible-light photocatalytic properties of the floating hollow glass microspheres – TiO2/Ag3PO4 composites

A novel floating visible-light photocatalyst (HGMs–TiO₂/Ag₃PO₄) composite was prepared using amino modified low-density hollow glass microspheres (HGMs) as carriers to disperse and support TiO₂ and Ag₃PO₄ photocatalysts. The surface morphology, crystal structure and optical properties of the HGMs–TiO₂/Ag₃PO₄ composites were characterized and the Ag₃PO₄ content on the surface of the microspheres was determined by atomic absorption spectrometry (AAS). Methylene blue (MB) was chose as the organic pollutant to investigate the visible-light catalytic properties of the HGMs–TiO₂/Ag₃PO₄ composites. For HGM composite photocatalysts, when the theoretical mass ratio of TiO₂ to Ag₃PO₄ on the surface of HGMs is 1 : 1.5, the visible-light catalytic activity of the composite is superior to pure Ag₃PO₄ and a TiO₂/Ag₃PO₄ photocatalyst with a mass ratio of 1 : 1.5 under the same conditions, due to the increased light-contact area and the photocatalytic active sites, since the TiO₂ and Ag₃PO₄ particles can be well dispersed on the surface of the floating HGMs. Furthermore, the deposits of TiO₂ and Ag₃PO₄ on the HGM surface form a heterostructure, facilitating the separation of electron–hole (e⁻ – h⁺) in the energy band, and elevating the photocatalytic activity and cycle stability of Ag₃PO₄. This work indicates that floating HGMs–TiO₂/Ag₃PO₄ composites could become a promising photocatalyst for organic dye removal due to the low cost and high visible-light responsiveness.

The amino modified low-density hollow glass microspheres were used as carriers of TiO₂ and Ag₃PO₄ photocatalysts to prepare the floating visible-light photocatalyst composite.     

Enhanced photocatalytic activity of TiO2/UiO-67 under visible-light for aflatoxin B1 degradation

TiO₂ has great potential in photocatalytic degradation of organic pollutants, but poor visible light response and low separation efficiency of photogenerated electron–hole pairs limit its wide applications. In this study, we have successfully prepared TiO₂/UiO-67 photocatalyst through an in situ solvothermal method. The degradation rate of aflatoxin B1 (AFB1) is 98.9% in only 80 min, which is superior to the commercial P25, commercial TiO₂ and most of reported photocatalysts under visible light irradiation. In addition, the TiO₂/UiO-67 photocatalyst showed excellent recyclability. We demonstrated that the enhanced photocatalytic mechanism was owing to the heterojunction between TiO₂ and UiO-67, which enhanced effectively the separation photogenerated charge carriers and visible light response. The free radical trapping tests demonstrated that superoxide radicals (˙O₂⁻), holes (h⁺) and hydroxyl radicals (˙OH) were the main active species and then oxidized AFB1 to some small molecules.

Enhanced photocatalytic activity of TiO₂/UiO-67 under visible-light for aflatoxin B1 degradation.     

A facile approach to synthesize CdS–attapulgite as a photocatalyst for reduction reactions in water

At room temperature, a facile approach has been utilized for preparing novel CdS–attapulgite (CdS–ATP) composites and the composites were applied in photocatalytic reduction of p-nitrophenol and Cr(vi). The effect of ATP on the photocatalytic activity of the CdS–ATP composites were studied by controlling the mass ratio of attapulgite. The results showed that the CdS–20%ATP composite has an excellent photocatalytic activity. In order to figure out the key to improve the photocatalytic efficiency, the prepared composites were characterized by Brunauer–Emmett–Teller (BET) specific surface area, UV-vis diffuse reflectance spectroscopy (DRS) and electrochemical impedance spectroscopy (EIS). The superior photocatalytic performance of the CdS–20%ATP composite can be ascribed to the existence of the ATP which can fix the CdS and prevent agglomeration. The interaction between ATP and CdS in the composites facilitates the electron transfer and also promoted their photocatalytic performance. This work provides us with some significant guidance in the development of CdS–ATP composite photocatalysts.

The application of CdS–attapulgite composites in photocatalytic reduction of p-nitrophenol and Cr(vi) demonstrated that the attapulgite could overcome the limitations of CdS.     

The simultaneous removal of heavy metals and organic contaminants over a Bi2WO6/mesoporous TiO2 nanotube composite photocatalyst

In this study, Bi₂WO₆/mesoporous TiO₂ nanotube composites (BWO/TNTs) were successfully synthesized to remove the heavy metal Cr(vi) and refractory organic compound dibutyl phthalate (DBP) from contaminated water under visible light. Coupling TNTs with BWO can greatly improve the photocatalytic activity of the catalyst for treating Cr(vi)–DBP mixed pollutants because of synergetic effects from Cr(vi) and DBP. Specifically, the visible-light photocatalytic activities of 3% BWO/TNTs for removing DBP and Cr(vi) from mixed pollutant solutions were 10.8 and 3.8 times higher than those of BWO. Firstly, this system can take full advantage of charge carriers and can spatially separate reduction sites and oxidation sites in the photocatalyst. Secondly, TNTs has a unique multiscale channel structure that can enhance mass transfer and light utilization. These characteristics lead to very obvious photocatalytic activity improvements. In addition, the BWO/TNTs composite photocatalysts exhibited excellent stability and durability under visible and UV light irradiation. This work demonstrated a feasible method for fabricating composite photocatalysts and applied them to the simultaneous removal of heavy metal and refractory organic pollutants from contaminated water.

In this study, Bi₂WO₆/mesoporous TiO₂ nanotube composites (BWO/TNTs) were successfully synthesized to remove the heavy metal Cr(vi) and refractory organic compound dibutyl phthalate (DBP) from contaminated water under visible light.     

Highly efficient visible light active Cu–ZnO/S-g-C3N4 nanocomposites for efficient photocatalytic degradation of organic pollutants

The photocatalytic activity of photocatalysts is severely hampered by limited visible light harvesting and unwanted fast recombination of photogenerated e⁻ and h⁺. In the current study, the photocatalytic efficiency of Cu–ZnO/S-g-C₃N₄ (CZS) nanocomposites was investigated against MB dye. The composite materials were designed via chemical co-precipitation method and characterised by important analytical techniques. Distinctive heterojunctions developed between S-g-C₃N₄ and Cu–ZnO in the CZS composite were revealed by TEM. The synthesized composites exhibit a huge number of active sites, a large surface area, a smaller size and better visible light absorption. The considerable enhancement in the photocatalytic activity of CZS nanocomposites might be accredited to the decay in the e–h pair recombination rate and a red shift in the visible region, as observed by PL and optical analysis, respectively. Furthermore, the metal (Cu) doping into the S-g-C₃N₄/ZnO matrix created exemplary interfaces between ZnO and S-g-C₃N₄, and maximized the photocatalytic activity of CZS nanocomposites. In particular, CZS nanocomposites synthesized by integrating 25% S-g-C₃N₄ with 4% Cu–ZnO (CZS-25 NCs) exhibited the 100% photocatalytic degradation of MB in 60 minutes under sunlight irradiation. After six cycles, the photocatalytic stability of CZS-25 NCs was excellent. Likewise, a plausible MB degradation mechanism is proposed over CZS-25 NCs based on photoluminescence and reactive species scavenger test observation. The current research supports the design of novel composites for the photocatalytic disintegration of organic contaminants.

The photocatalytic activity of photocatalyst is severely hampered by limited visible light harvesting and unwanted fast recombination of photogenerated e⁻ and h⁺.     

Flake-like InVO4 modified TiO2 nanofibers with longer carrier lifetimes for visible-light photocatalysts

Highly efficient solar light absorption capabilities and quantum yields in photocatalysts are key to their application in photocatalytic fields. Towards this end, TiO₂/InVO₄ nanofibers (NFs) have been designed and fabricated successfully by a one-pot electrospinning process. The resulting TiO₂/InVO₄ NFs display excellent visible-light photocatalytic activity, owing to their prominent visible-light absorption and electron–hole separation properties. Time-resolved transient PL spectroscopy demonstrated that the TiO₂/InVO₄ NFs display longer emission decay times (22.0 ns) compared with TiO₂ NFs (15.5 ns), implying that the heterojunction can remarkably suppress the electron–hole recombination and promote the carrier transfer efficiency. With tailored heterostructure features, TiO₂/InVO₄ NFs exhibit superior visible-light photodegradation activity, and after 80 min of visible-light irradiation, almost 95% of RhB molecules can be decomposed by TiO₂/InVO₄ NFs, while only 18% of RhB molecules can be decomposed by pure TiO₂ NFs.

TiO₂/InVO₄ nanofibers have been designed and fabricated successfully by one-pot electrospinning process, which display longer carrier lifetime (22 ns) and enhanced visible-light photocatalytic activity.     

Novel N-doped ZrO2 with enhanced visible-light photocatalytic activity for hydrogen production and degradation of organic dyes

Two new types of N-doped ZrO₂ photocatalysts ZON and AZON have been synthesized using ethylenediamine as the nitrogen source by a facile and low-cost sol–gel method. The N-doped ZrO₂ samples have been characterized using various techniques including X-ray diffraction (XRD), UV-Vis spectroscopy, Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), photoluminescence spectroscopy (PL) and N₂ adsorption–desorption tests. The XRD analysis shows that the crystallinity of ZON samples calcined at 400–600 °C can be indexed to monoclinic ZrO₂; while the AZON samples calcined at 400–550 °C only show amorphous diffraction patterns. The UV-Vis response of both N-doped ZrO₂ samples can be extended to the visible light regime. The high resolution XPS spectra indicate that N element has been doped in the lattice of ZrO₂. Visible-light photocatalytic reactions using the N-doped ZrO₂ photocatalysts (i.e. ZON, AZON) calcined at 450 °C show the highest hydrogen production rate (2.12 mmol g⁻¹ h⁻¹) and best methylene orange degradation performance due to substitutional N-doping of the ZrO₂. The novel N-doped ZrO₂ materials are demonstrated to be very promising photocatalysts with enhanced visible-light photocatalytic activity. Our results provide useful insights into the development of novel photocatalytic materials for hydrogen production and degradation of organic wastes by narrowing the wide bandgap of semiconductors with high photocatalytic activity under UV-Vis light.

Two new types of N-doped ZrO₂ photocatalysts ZON and AZON have been synthesized using ethylenediamine as the nitrogen source by a facile and low-cost sol–gel method.     

Facile synthesis of multi-type carbon doped and modified nano-TiO2 for enhanced visible-light photocatalysis

Nano-TiO₂ is a type of environment-friendly and inexpensive substance that could be used for photocatalytic degradation processes. In this study, the multi-type carbon species doped and modified anatase nano-TiO₂ was innovatively synthesized and developed to overcome the deficiency of common nano-TiO₂ photocatalysts. The multi-type carbon species were derived from tetrabutyl titanate and ethanol as the internal and external carbon sources, respectively. Meanwhile, diverse characterization methods were applied to investigate the morphology and surface properties of the photocatalyst. Finally, the visible-light photocatalytic degradation activity of the collected samples was evaluated by using methyl orange as a model pollutant. The promotion mechanism of multi-type carbon species in the photocatalytic process was also discussed and reported. The results in this work show that the doping and modification of multi-type carbon species successfully narrows the bandgap of nano-TiO₂ to expand the light absorption range, reduces the valence band position to improve the oxidation ability of photogenerated holes, and promotes the separation of photogenerated charge carriers to improve quantum efficiency. In addition, the further modification of the external carbon source can promote the surface adsorption of MO and stabilize the multi-type carbon species on the surface of nano-TiO₂.

The synergistic modification of nano-TiO₂ by multi-type carbon species results in excellent and stable visible-light photocatalytic degradation activity.     

Ternary dual Z-scheme graphitic carbon nitride/ultrathin metal–organic framework nanosheet/Ag3PO4 photocatalysts for boosted photocatalytic performance under visible light

Ternary graphitic carbon nitride/ultrathin metal–organic framework nanosheet/Ag₃PO₄ (CNUA) composite photocatalysts were prepared under ultrasonic irradiation in tetrahydrofuran. The aim was to use them as photocatalysts for the degradation of organic pollutants in water. The crystal structure, surface morphology, optical properties, and chemical composition of the photocatalytic materials were investigated using X-ray diffraction, scanning electron microscopy, UV-vis diffuse reflectance spectroscopy, and X-ray photoelectron spectroscopy (XPS). The XPS analysis revealed the formation of Ag nanoparticles, which play an important role as an electronic mediator and photosensitizer in the composite during the synthesis. The photocatalytic activity of the composites in the degradation of 2-chlorophenol (2-CP) under visible light (>420 nm) was evaluated. Among the synthesized photocatalysts, the optimized CNUA with 10 wt% of g-C₃N₄ with respect to Ag₃PO₄ (CN10UA), exhibited the best photocatalytic performance in the degradation of 2-CP, which was almost decomposed completely upon ∼5 min of visible-light irradiation. Furthermore, the stability of the CN10UA photocatalyst could be maintained at a high level even after four cycling experiments, while that of pure Ag₃PO₄ declined significantly. The enhanced photocatalytic performance results from efficient charge separation through the dual Z-scheme mechanism involving Ag(0) bridges in the g-C₃N₄/Ag/Ag₃PO₄ and Ag₃PO₄/Ag/UMOFN pathways. The analysis of the photoluminescence of the catalysts also provided evidence for charge transport via the dual Z-scheme mechanism. In addition, radical scavenging tests confirmed that h⁺ and O₂˙⁻ are the main radical reactive species responsible for the photodegradation of 2-CP. The findings of this study enhance our understanding of the construction and mechanism of dual Z-scheme-type photocatalysts.

The enhanced photocatalytic activity of CN10UA results from fast charge transport through dual Z-scheme channels.     

Hydrogen production from methanol aqueous solution by ZnO/Zn(OH)2 macrostructure photocatalysts

Photocatalytic H₂ generation was studied for a series of ZnO/Zn(OH)₂ macrostructure photocatalysts. Different ZnO/Zn(OH)₂ macrostructures were prepared through a one-step hydrothermal method by adjusting the pH values of the solution and the concentration of dodecyl sulfate. Three different morphologies of the ZnO/Zn(OH)₂ macrostructure were synthesized and studied using SEM and XRD. The reflectance spectra revealed that the cone shaped ZnO/Zn(OH)₂ macrostructure (ZnO-C) had the lowest reflectivity of UV light. It was found that the photoelectronic properties depend on the morphology of the ZnO/Zn(OH)₂ macrostructures. The photocatalytic activity of these ZnO/Zn(OH)₂ macrostructure hybrids (about 0.070 mmol g⁻¹ h⁻¹) were higher than that observed for ZnO nanorods (0.050 mmol g⁻¹ h⁻¹). These results suggest the substantial potential of metal oxide materials with macrostructures in photocatalytic water splitting applications.

ZnO/Zn(OH)₂ macrostructure photocatalysts prepared using a one-step hydrothermal method demonstrated highly efficient photocatalytic hydrogen production.     

Synthesis and photocatalytic properties of three dimensional laminated structure anatase TiO2/nano-Fe0 with exposed (001) facets

Three dimensional laminated structure anatase TiO₂/nano-Fe⁰ with exposed (001) facets used as photocatalysts were synthesized by a two-step solvothermal route and a liquid phase reduction deposition method. The resulting samples were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, ultraviolet-visible diffuse reflectance spectroscopy, scanning electron microscopy, transmission electron microscopy and selected-area electron diffraction. Characterization and experimental results indicated that the three dimensional laminated structure of anatase TiO₂ was assembled by two dimensional TiO₂-sheets with a thickness of approximately 30 nm. The three dimensional laminated structure anatase TiO₂/nano-Fe⁰ photocatalysts with improved visible-light responsive capability, high charge-hole mobility, and low electron–hole recombination exhibited higher photocatalytic performance in the photocatalytic degradation of methylene blue. The composite of nano-Fe⁰ and TiO₂ could effectively promote the generation of hydroxyl radicals (˙OH) with a synergistic effect and Photo-Fenton theory. This study provided new insights into the fabrication and practical application of high-performance photocatalysts in degrading organic pollutants.

Three dimensional laminated structure anatase TiO₂/nano-Fe⁰ with exposed (001) facets were successfully synthesized, which exhibited higher photocatalytic performance in the photocatalytic degradation of methylene blue.     

Construction of a novel two-dimensional AgBiO3/BiOBr step-scheme heterojunction for enhanced broad-spectrum photocatalytic performance

Efficient S-scheme heterojunction photocatalysts were prepared through in situ growth of AgBiO₃ on BiOBr. The self-assembled hierarchical structure of AgBiO₃/BiOBr was formed from flower-like AgBiO₃ and plate-like BiOBr. The optimized AgBiO₃/BiOBr heterojunction possessed excellent visible-light photocatalytic degradation efficiency (83%) for ciprofloxacin (CIP) after 120 min, with 1.46- and 4.15-times higher activity than pure AgBiO₃ and BiOBr, respectively. Furthermore, the removal ratio of multiple organic pollutants including tetracycline, Rhodamine B, Lanasol Red 5B and methyl orange was also investigated. Environmental interference experiments demonstrated that high pollutant concentrations, low photocatalyst dose and the addition of ions (SO₄²⁻, PO₄³⁻, HPO₄²⁻, H₂PO₄⁻) inhibited the photocatalytic activities. Subsequently, a simultaneous degradation experiment showed the competitive actions between CIP and RhB for radicals, decreasing the photocatalytic activity of CIP. Furthermore, trapping and electron spin resonance experiments showed that h⁺ and ˙O₂⁻ played a certain role in the degradation process and that ˙OH acted as assistant.

Efficient S-scheme heterojunction photocatalysts were prepared through in situ growth of AgBiO₃ on BiOBr.     

Enhanced photocatalytic H2 evolution over covalent organic frameworks through an assembled NiS cocatalyst

Covalent organic frameworks (COFs) have been investigated in the field of photocatalysts for H₂ evolution because of their crystalline structure and diversity. However, most of them need the help of noble metals as co-catalysts to realize a high hydrogen evolution. Herein, we chose typical COFs as a platform and constructed NiSX-BD (X: weight fraction of NiS) composites by assembling NiS at room temperature. The NiS nanoparticles are shown to tightly adhere to the COFs surface. Under visible light irradiation (wavelength > 420 nm), the optimized sample with 3 wt% NiS loading exhibits a photocatalytic H₂ evolution rate of 38.4 μmol h⁻¹ (3840 μmol h⁻¹ g⁻¹), which is about 120 folds higher than that of the pure TpBD-COF and better than TpBD-COF/Pt with the same Pt loading (3 wt%). NiS3-BD shows stable hydrogen evolution in at least six consecutive cycle tests totaling 18 h. Further investigation reveals that the loaded NiS can facilitate the transfer of photogenerated electrons from TpBD-COF to the co-catalyst, leading to efficient and high photocatalytic activity. Combining the significant feature of COFs, this study opens up a feasible avenue to boost the photocatalytic H₂ performance by constructing the synergetic effects between COFs and cost-effective material.

We constructed a novel hybrid photocatalyst by assembling NiS through a milder method. Under visible light irradiation, controlled NiS/TpBD-COF composites can readily optimize photocatalytic performances without a noble cocatalyst.     

Synergetic effect of photocatalysis and peroxymonosulfate activated by MFe2O4 (M = Co,Mn, or Zn) for enhanced photocatalytic activity under visible light irradiation

Nanosized MFe₂O₄ (M = Co, Mn, or Zn) photocatalysts were synthesized via a simple sol–gel method. MFe₂O₄ photocatalysts exhibited lower photocatalytic activity for the degradation of levofloxacin hydrochloride under visible light irradiation. For enhancement of photocatalytic activity, MFe₂O₄ was used to activate peroxymonosulfate and degrade levofloxacin hydrochloride under visible light irradiation. The influences of peroxymonosulfate dosage, levofloxacin hydrochloride concentration, pH value, and temperature on peroxymonosulfate activation to degrade levofloxacin hydrochloride were investigated in detail. The mechanism of activation of peroxymonosulfate by MFe₂O₄ was proposed and proved by radical quenching experiments, electron spin resonance analysis, X-ray photoelectron spectroscopy, electrochemical impedance spectroscopy, and transient photocurrent responses. The combined activation effects of photogenerated e⁻/h⁺ and transition metals on peroxymonosulfate to produce sulfate radical clearly enhanced the degradation efficiency.

The combined activation effects of photogenerated e⁻/h⁺, Fe, Co, Mn, and Zn on peroxymonosulfate to produce SO₄˙⁻ clearly enhanced the degradation efficiency.     

Concurrent and dual N-doping of graphene/ZnO nanocomposites for enhanced Cr(vi) photoreduction activity under visible-light irradiation

Simultaneous and dual N-doping of two components in reduced graphene oxide/ZnO nanocomposites were successfully achieved by thermally annealing a GO/Zn(HCO₃)₂ precursor in an NH₃ atmosphere. In this facile preparative procedure, NH₃ was used not only as the reagent for in situ reduction of GO but also as the source for N-doping. Detailed characterizations showed that the nitrogen element was successfully and simultaneously incorporated into the crystal lattice of ZnO and graphene phases in the composites and the formation of oxygen vacancies was also achieved. The photocatalytic tests indicated that N-doping of graphene/ZnO (NG/NZO) nanocomposites exhibited the higher Cr(vi) photoreduction activity than graphene/ZnO, virgin N-doped ZnO (NZO) and the sample prepared via simple physically mixing. The mechanistic study demonstrated that the remarkable photocatalytic activity of NG/NZO photocatalysts was due to the synergistic effect of simultaneously N-doping two phases in the composites and the existence of oxygen vacancies, and mainly included the increased electrical conductivity of N-doped graphene (NG), the expansion of visible light harvesting capability of NZO and the effective separation of electron–hole pairs of the oxygen vacancies.

Simultaneous and dual N-doping of two components in reduced graphene oxide/ZnO nanocomposites were successfully achieved by thermally annealing a GO/Zn(HCO₃)₂ precursor in an NH₃ atmosphere.     

Unbiased spontaneous solar hydrogen production using stable TiO2–CuO composite nanofiber photocatalysts

We report on the optimization of electrospun TiO₂–CuO composite nanofibers as low-cost and stable photocatalysts for visible-light photocatalytic water splitting. The effect of different annealing atmospheres on the crystal structure of the fabricated nanofibers was investigated and correlated to the photocatalytic activity of the material. The presence of CuO resulted in narrowing the bandgap of TiO₂ and shifting the absorption edge into the visible region of the light spectrum. The effect of incorporating CuO within TiO₂ nanofibers on the crystal structure and composition was also investigated using X-ray diffraction (XRD), electron paramagnetic resonance (EPR), and X-ray photoelectron spectroscopy (XPS) techniques. The fabricated TiO₂–CuO composite nanofibers showed 117% enhancement in the amount of hydrogen evolved during the photocatalytic water splitting process compared to pure TiO₂. This enhancement was related to the created shallow defect states that facilitate charge transfer from TiO₂ to CuO and distinct characteristics of the composite nanofibers, such as the high surface area and directional charge transfer. The study showed that Cu is a promising alternative to noble metals as a catalyst in photocatalytic water splitting, with the advantage of being an Earth abundant element and a relatively cheap material.

We report on the optimization of electrospun TiO₂–CuO composite nanofibers as low-cost and stable photocatalysts for visible-light photocatalytic water splitting.