Visible light-mediated photocatalytic oxidative cleavage of activated alkynes via hydroamination: a direct approach to oxamates

The direct oxidative cleavage of activated alkynes via hydroamination has been described using organic photocatalyst under visible-light irradiation at room temperature. In this reaction, the single electron oxidation of an in situ formed enamine followed by radical coupling with an oxidant finally delivers the oxamate. The key features of this photocatalytic reaction are the mild reaction conditions, metal-free organic dye as a photocatalyst, and TBHP playing a dual role as “O” source and for the regeneration of the photocatalyst.

The direct oxidative cleavage of activated alkynes via hydroamination has been described using organic photocatalyst under visible-light irradiation at room temperature.     

Atomic-scale synthesis of nanoporous gallium–zinc oxynitride-reduced graphene oxide photocatalyst with tailored carrier transport mechanism

Surface modified gallium–zinc oxynitride solid solution exhibited outstanding stability and visible-light activity for water splitting. However, the considerable rate of photo-induced charge recombination and the low surface area of the bulk photocatalyst limited its performance. Here, an efficient technique is proposed for the synthesis of a nanoporous oxynitride photocatalyst and its graphene-hybridized material. The nanoporous oxynitride photocatalyst was prepared via a nanoscale solid-state route, using microwave irradiation as an intermolecular-state activation method, Ga³⁺/Zn²⁺ layered double hydroxide as an atomic-level uniform mixed-metal precursor, and urea as a non-toxic ammonolysis soft-template. The graphene-hybridized photocatalyst was fabricated using a facile electrostatic self-assembly technique. The photocatalytic activity of the synthesized graphene hybridized nanoporous oxynitride photocatalyst was systematically improved through shortening the majority-carrier diffusion length and enhancing the density of active hydrogen evolution sites within the quasi-three-dimensional nanostructure, reaching 7.5-fold sacrificial photocatalytic hydrogen evolution, compared to the conventional 1 wt% Rh-loaded oxynitride photocatalyst.

Synthesis of nanoporous GaZnON-RGO composite photocatalyst with enhanced capacity for HER active site and improved visible light hydrogen evolution performance is reported.     

Visible-light-driven CQDs@MIL-125(Ti) nanocomposite photocatalyst with enhanced photocatalytic activity for the degradation of tetracycline

In the present study, a novel photocatalyst, CQDs@MIL-125(Ti) (CQDs = carbon quantum dots), was prepared via a solvothermal procedure. The photocatalytic properties were tested by the degradation of tetracycline (TC) with a 250 W Xe lamp (λ > 420 nm). Compared with pure MIL-125(Ti), the 10 wt% CQDs@MIL-125(Ti) photocatalyst can significantly improve the degradation process of TC, and the degradation efficiency can reach 90% within 4 h. The enhancement in the photocatalytic performance is due to the CQDs, which can promote the absorption of visible light and also efficiently accelerate the separation of photogenerated electron–hole pairs. We have also demonstrated that superoxide radicals (·O₂⁻) and holes (h⁺) play crucial roles in the photocatalytic degradation of TC through capture experiments. The current work provides a new idea for constructing high-efficiency photocatalysts based on MIL-125(Ti).

A novel CQDs@MIL-125(Ti) photocatalyst had been synthesized by a facile solvothermal process for the degradation of TC. The possible degradation mechanism was proposed based on the active species trapping experiments.     

Effective photoreduction of graphene oxide for photodegradation of volatile organic compounds

Nowadays, humans spend most of their time indoors and are frequently exposed to volatile organic compounds (VOCs) from various sources. The photocatalytic oxidation (PCO) method is a relatively more efficient method than the adsorption method for removing VOCs from the environment. In this work, graphene oxide (GO) was partially reduced via photoreduction under ultraviolet light (UV-A) irradiation and then used as a photocatalyst to degrade VOCs. After photoreduction, the band gap of the partially reduced graphene oxide (PRGO) decreased from 3.5–4.5 eV to 3.1–4.0 eV. Methanol vapour, which acts as a model VOC, was photodegraded using the PRGO. The effectiveness of the PRGO was mainly due to the removal of oxygen functional groups and restoration of the sp² domain. This lowered the band gap and slowed down the electron recombination rate, which resulted in a higher photocatalytic activity. The photocatalytic activity of PRGO followed pseudo-first order kinetics, with a rate constant of 0.0025 min⁻¹, and it could be reused for five cycles without any significant loss in the photocatalytic activity. This study demonstrates the potential of PRGO as a versatile and stable metal-free photocatalyst to remove indoor pollutants.

Photoreduced graphene oxide has a narrower band gap and better photocatalytic oxidation to degrade methanol.     

Photocatalytic turnover of CO2 under visible light by [Re(CO)3(1-(1,10) phenanthroline-5-(4-nitro-naphthalimide))Cl] in tandem with the sacrificial donor BIH

Optimized photocatalytic conversion of CO₂ requires new potent catalysts that can absorb visible light. The photocatalytic reduction of CO₂ using rhenium(i) has been demonstrated but suffers from low turnover. Herein, we describe a [Re(CO)₃(1-(1,10)phenanthroline-5-(4-nitro-naphthalimide))Cl] photocatalyst, which when combined with the sacrificial donor 1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzo[d]imidazole, results in selective production of formic acid and a high turnover number of 533 and turnover frequency of 356 h⁻¹. Single-crystal X-ray diffraction and DFT studies are also discussed.

Rhenium based photocatalytic conversion CO₂ to formate in the visible region with excellent turnover.     

Pt–Nix alloy nanoparticles: a new strategy for cocatalyst design on a CdS surface for photo-catalytic hydrogen generation

Solar photocatalytic water splitting for the production of hydrogen has been a core aspect for decades. A highly active and durable photocatalyst is crucial for the success of the renewable hydrogen economy. To date, the development of highly effective photocatalysts has been seen by the contemporary research community as a grand challenge. Thus, herein we put forward a sincere attempt to use a Pt–Ni_x alloy nanoparticle (NP) cocatalyst loaded CdS photocatalyst ((Pt–Ni_x)/CdS) for photocatalytic hydrogen production under visible light. The Pt–Ni_x alloy NP cocatalyst was synthesized using a one-pot solvothermal method. The cocatalyst nanoparticles were deposited onto the surface of CdS, forming a Pt–Ni_x/CdS photocatalyst. Photocatalytic hydrogen production was carried out using a 300 W Xe light equipped with a 420 nm cut-off filter. The H₂ evolution rate of the Pt–Ni₃/CdS photocatalyst can reach a value as high as 48.96 mmol h⁻¹ g⁻¹ catalyst, with a quantum efficiency of 44.0% at 420 nm. The experimental results indicate that this Pt–Ni₃/CdS photocatalyst is a prospective candidate for solar hydrogen generation from water-splitting.

In this report, PtNi_x alloy NPs coupled with a CdS photocatalyst for photocatalytic hydrogen generation under visible light have been explored.     

Enhanced photocatalytic activity of a B12-based catalyst co-photosensitized by TiO2 and Ru(ii) towards dechlorination

A novel hybrid photocatalyst denoted as B₁₂–TiO₂–Ru(ii) was prepared by co-immobilizing a B₁₂ derivative and trisbipyridine ruthenium (Ru(bpy)₃²⁺) on the surface of a mesoporous anatase TiO₂ microspheres and was characterized by DRS, XRD, SEM and BET et al. By using the hybrid photocatalyst, DDT was completely didechlorinated and a small part of tridechlorinated product was also detected in the presence of TEOA only after 30 min of visible light irradiation. Under simulated sunlight, the hybrid exhibited a significantly enhanced photocatalytic activity for dechlorination compared with B₁₂–TiO₂ under the same condition or itself under visible light irradiation due to the additivity in the contribution of UV and visible part of the sunlight to the electron transfer. In addition, this hybrid catalyst can be easily reused without loss of catalytic efficiency. This is the first report on a B₁₂-based photocatalyst co-sensitized by two photosensitizers with wide spectral response.

The additivity of the contribution of the UV and visible parts of sunlight to electron transfer was confirmed in the B₁₂–TiO₂–Ru(ii) photocatalytic system.     

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.     

Ultrathin Ni(OH)2 nanosheets: a new strategy for cocatalyst design on CdS surfaces for photocatalytic hydrogen generation

Ultrathin metal materials exhibit quantum size and surface effects that give rise to unique catalytic properties. In this paper, we report a facile liquid synthesis method for polyvinylpyrrolidone (PVP, K30) capped ultrathin Ni(OH)₂ nanosheets with lamellar structure. The as-prepared ultrathin Ni(OH)₂ nanosheets coupled with CdS nanorods exhibit excellent activity in hydrogen generation from water splitting under visible light. The H₂ evolution rate of Ni(OH)₂/CdS, 40.18 mmol h⁻¹ g_Cat.⁻¹ with a quantum efficiency of 66.1% at 420 nm, is ca. 1.5 times that of Pt/CdS with an optimal loading amount (1.25 wt%) under the same reaction conditions. Considering the cost of photocatalysts, the ultrathin Ni(OH)₂ nanosheet coupled CdS photocatalyst may have a promising commercial application in photocatalytic hydrogen production.

In this report, ultrathin Ni(OH)₂ nanosheets coated CdS photocatalyst for photocatalytic hydrogen generation under visible light has been explored.     

Facile construction of a ZIF-67/AgCl/Ag heterojunction via chemical etching and surface ion exchange strategy for enhanced visible light driven photocatalysis

It is of great importance to design and fabricate heterojunction photocatalysts to improve photocatalytic performance. In this work, a novel ZIF-67/AgCl/Ag heterojunction photocatalyst was successfully synthesized by a facile chemical etching, deposition–precipitation, light-induced reduction approach. After chemical etching by a AgNO₃ precursor, the crystal size of ZIF-67 decreased remarkably together with the replacement of Co²⁺ in the framework of ZIF-67 by Ag⁺via surface ion exchange. As a result, optical and electrochemical measurements indicated that the separation efficiency of light-induced electrons and holes obviously increased due to the formation of a ZIF-67/AgCl/Ag heterojunction and the surface plasmon resonance of Ag⁰. Meanwhile, the corresponding kinetic rate constant of ZIF-67/AgCl/Ag was estimated to be 0.1615 min⁻¹, which was 17, 7.76 and 2.67 times as high as that of individual ZIF-67, AgCl and ZIF-67/AgCl, respectively. The ZIF-67/AgCl/Ag photocatalyst also exhibited good stability and reusability in the process of photodegradation. This work demonstrated a high efficiency photocatalyst for providing new sights into the preparation of a highly efficient MOF-based heterojunction photocatalyst and its potential applications in water purification.

It is of great importance to design and fabricate heterojunction photocatalysts to improve photocatalytic performance.     

A one-pot synthesis of AgBr/Ag3PO4 composite photocatalysts

In this study, an AgBr/Ag₃PO₄ (ABAP) photocatalyst has been prepared via a facile one-pot anion-exchange method. SEM, XRD, XPS and UV-Vis DRS characterization techniques are carried out to study the structural and physicochemical characteristics of the AgBr/Ag₃PO₄ composites. The ABAP photocatalyst exhibited outstanding photocatalytic capability for the photodegradation of rhodamine B (RhB) under visible light irradiation. The optimal ABAP-48% composite displayed the highest photocatalytic activity; a complete degradation was attained in 25 min under visible light irradiation. The excellent stability and reusability of ABAP catalysts were examined by five subsequent runs. A probable degradation mechanism of ABAP composites was carefully surveyed. Furthermore, radical trapping experiments confirmed that the ˙O₂⁻ radical was the main active species in the photodegradation reaction.

In this study, an AgBr/Ag₃PO₄ (ABAP) photocatalyst has been prepared via a facile one-pot anion-exchange method.     

Two dimensional ZnO/AlN composites used for photocatalytic water-splitting: a hybrid density functional study

Using hybrid density functionals, we study the interfacial interactions and electronic properties of ZnO/AlN composites with the consideration of rotation angles and biaxial strains in order to enhance the photocatalytic performance for water-splitting. The different rotated composites, and −2% strained, original, and 2% strained ZnO/AlN composites can be easily prepared owing to the negative interface formation energies. The bandgaps and band alignments of ZnO/AlN composites can be significantly tuned by biaxial strains. Particularly, the appropriate bandgap for visible light absorption, proper band alignment for spontaneous water-splitting, and the formed electric field promoting photoinduced carrier separation make the 2% strained ZnO/AlN composite a potential candidate for photocatalytic water-splitting. This work shines some light on designing two dimensional heterostructured photocatalysts.

With adapted bandgap for absorbing visible light, suitable band edge positions, and induced electric field inhibiting photoexcited carrier recombination, 2% strained ZnO/AlN composite is a promising water-splitting photocatalyst.     

2D–3D graphene-coated diatomite as a support toward growing ZnO for advanced photocatalytic degradation of methylene blue

In this work, a diatomite@graphene@ZnO (ZGD) photocatalyst was synthesized by chemical vapor deposition and hydrothermal methods and used for the photocatalytic degradation of methylene blue. The characterization of the prepared nanocomposite was performed by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, X-ray diffraction (XRD), and N₂ adsorption–desorption techniques. Ultraviolet-visible diffuse reflectance spectroscopy (DRS) showed that the prepared ZGD photocatalyst enhanced the absorption of visible light and induced a red-shift. Photoluminescence spectroscopy (PL) revealed that the recombination of electron and hole pairs can be effectively suppressed. Besides, the synergistic effect of diatomite and graphene avoids the agglomeration of ZnO, increases the number of surface adsorption sites, and limits the electron transport, consequently improving the photocatalytic activity of ZnO. When ZGD-3 was UV-irradiated (λ = 663 nm) for 90 minutes, the degradation effectiveness of methylene blue (MB) was 100%. After the fifth repetition, the photocatalytic degradation efficiency was always greater than 95%. Simply put, the ZGD nanocatalyst can be used as an efficient photocatalyst for dye wastewater treatment.

In this work, a diatomite@graphene@ZnO (ZGD) photocatalyst was synthesized by chemical vapor deposition and hydrothermal methods and used for the photocatalytic degradation of methylene blue.     

Synthesis of Gd/N co-doped ZnO for enhanced UV-vis and direct solar-light-driven photocatalytic degradation

The construction of a UV-Vis and direct sunlight functioning photocatalyst is a puzzling task for organic pollutant removal. Herein, we have fabricated Gd/N co-doped ZnO nanoparticles for the first-time using a simple co-precipitation method for photocatalytic degradation application. The heteroatom doping enhances the light absorption ability and acts as a photo-induced electron–hole separator by creating a trap state. Co-doped ZnO shows comparatively high photocatalytic degradation efficiency of about 87% and 93% under UV-Vis and direct solar light respectively. Moreover, the prepared photocatalyst exhibits excellent stability for the recycling process. Hence, we believe that this heteroatom co-doped ZnO photocatalyst is an auspicious material for the photocatalytic organic pollutant degradation reaction.

The construction of a UV-Vis and direct sunlight functioning photocatalyst is a puzzling task for organic pollutant removal.     

Enhanced charge separation and increased oxygen vacancies of h-BN/OV-BiOCl for improved visible-light photocatalytic performance

The introduction of oxygen vacancies (OVs) on the surface of photocatalysts has already been proven to be an effective way to extend the light response to visible light and trap charge carriers, thereby promoting the photocatalytic performance. In this study, h-BN/OV-BiOCl composites were prepared using hexagonal boron nitride (h-BN) to further improve the visible-light photocatalytic activity of oxygen-vacancy-enriched bismuth oxychloride (OV-BiOCl). The composition and morphology of these materials were investigated, and the photocatalytic performance experiments showed that the introduction of h-BN could significantly improve the visible-light photocatalytic activity of OV-BiOCl, which was 1.7 and 1.4 times that of pure OV-BiOCl for the degradation of rhodamine B (RhB) and bisphenol A (BPA) when the h-BN content was 5 wt%, respectively. The role of h-BN was comprehensively investigated, and the results revealed that the presence of negatively charged h-BN could improve the separation efficiency of photoinduced electrons (e⁻) and holes (h⁺) by promoting the migration of positively charged h⁺ to the surface of the photocatalyst, as expected. Moreover, the oxygen vacancies in OV-BiOCl were increased in the presence of h-BN; this favored the activation of more adsorbed O₂ for the oxidation of pollutants. Finally, a probable mechanism was proposed for the improved photocatalytic activity of the h-BN/OV-BiOCl composites. This study provides an insight into the roles of h-BN in oxygen-vacancy-enriched photocatalysts.

h-BN/OV-BiOCl composites were prepared to improve the visible-light photocatalytic activity of OV-BiOCl.     

Construction of novel Ag/HKUST-1/g-C3N4 towards enhanced photocatalytic activity for the degradation of pollutants under visible light

A novel Ag/metal–organic framework/graphitic carbon nitride (Ag/HKUST-1/g-C₃N₄, AHC) photocatalyst was prepared via an in situ growth strategy and photo-deposition technique for environmental remediation. The as-obtained samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), N₂ adsorption–desorption isotherm measurement, UV-vis diffuse reflection spectroscopy (UV-vis DRS), and photoluminescence (PL) spectroscopy. The results indicated that the hybrids have large surface area, mesoporous structure and enhanced visible-light absorption. The as-prepared hybrid samples exhibited considerable improvement in photocatalytic activity and stability for rhodamine B (RhB) degradation under visible light irradiation (λ > 420 nm). In addition, they also have good adsorption properties. Compared to the pure g-C₃N₄ and Ag/g-C₃N₄, the 5% AHC photocatalyst showed superior photocatalytic activity. Moreover, 5% AHC exhibits good photocatalytic activity even after four cycles. Additionally, the active species trapping and electron spin resonance (ESR) experiments indicated that h⁺ and ·OH were the main active species.

A novel AHC photocatalyst was prepared via in situ growth strategy and photo-deposition technique. The as-prepared hybrid samples have good photocatalytic activity and stability for Rh B degradation under visible-light irradiation.     

NiSe2/CdS composite nanoflakes photocatalyst with enhanced activity under visible light

Degrading organic pollutants using a photocatalyst under visible light is one of the effective ways to solve the increasingly serious environmental pollution problem. In this work, we have loaded a small amount of NiSe₂ nanoflakes on the surface of CdS using a simple and low-cost solvothermal synthesis method. The samples were characterized with detailed X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), electrochemical impedance spectroscopy (EIS), photocurrent, photoluminescence spectrometer (PL), photocatalytic properties, etc. The results show that a 2 mol% load of NiSe₂ increases the rate of degradation of Rhodamine B (RhB) to more than twice the original rate (0.01000 min⁻¹versus 0.00478 min⁻¹). Meanwhile, the sample has excellent stability. The improved photocatalytic properties can be attributed to the face-to-face contact between the nanoflakes, accelerated separation and transfer of photon-generated carriers. This work provides a suitable co-catalyst that can be used to optimize the performance of other photocatalytic materials.

The obtained NiSe₂/CdS composite nanoflakes exhibit greatly enhanced photocatalytic properties due to the accelerated separation of photon-generated carriers.     

Fabrication,characterization and high photocatalytic activity of Ag–ZnO heterojunctions under UV-visible light

Pure ZnO and Ag–ZnO nanocomposites were fabricated via a sol–gel route, and the obtained photocatalysts were characterized by XRD, SEM, TEM, BET, XPS, PL and DRS. The results showed that Ag⁰ nanoparticles deposit on the ZnO surface and Ag modification has negligible impact on the crystal structure, surface hydroxyl group content and surface area of ZnO. However, the recombination of photogenerated electrons and holes was suppressed effectively by Ag loading. The photocatalytic activity was investigated by evaluating the degradation of MB under xenon lamp irradiation as the UV-visible light source, and the results show that the photocatalytic activity of ZnO significantly improved after Ag modification. Ag–ZnO photocatalysts exhibit higher photocatalytic activity than commercial photocatalyst P25. The degradation degree of MB for 1%Ag–ZnO was 97.1% after 15 min. ˙O₂⁻ radicals are the main active species responsible for the photodegradation process, and Ag–ZnO heterojunctions generate more ˙O₂⁻ radicals, which is the primary reason for the improved photocatalytic performance.

Ag–ZnO heterojunction promotes the separation of photogenerated pairs and thus exhibits high catalytic activity under UV-visible light.     

Cadmium sulfide net framework nanoparticles for photo-catalyzed cell redox

A strategy for synthesizing cadmium sulfide net framework (CdS-NF) nanoparticles was developed in a water-based system under mild reaction conditions. The CdS-NFs have not only the excellent photocatalytic properties of CdS, but also the large surface area and diverse porous structures of a metal–organic framework. An Escherichia coli–CdS-NF hybrid system was constructed using NADH regeneration to promote the conversion of trimethylpyruvate acid to l-tert-leucine. The E. coli–CdS-NF system showed higher NAD⁺ recycling efficiency and substrate conversion rate than CdS QDs under visible light illumination. This work demonstrates a novel method for developing a brilliant coenzyme recycling photocatalyst in bio-redox reactions.

CdS net framework (CdS-NF) nanoparticles were synthesized under mild reaction conditions and used to construct an Escherichia coli–CdS-NF hybrid system which used NADH regeneration to promote the redox reaction.     

Improving the photocatalytic reduction of CO2 to CO for TiO2 hollow spheres through hybridization with a cobalt complex

A chemical system with enhanced efficiency for electron generation and transfer was constructed by the integration of TiO₂ hollow spheres with [Co(bipy)₃]²⁺. The introduction of [Co(bipy)₃]²⁺ remarkably enhances the photocatalytic activity of pristine semiconductor photocatalysts for heterogeneous CO₂ conversion, which is attributable to the acceleration of charge separation. Of particular interest is that the excellent photocatalytic activity of the heterogeneous catalysts can be utilised for a universal photocatalytic CO₂ reduction system. Yields of 16.8 μmol CO and 6.6 μmol H₂ can be obtained after 2 h of the photoredox reaction, and the apparent overall quantum yield was estimated to be 0.66% under irradiation at λ = 365 nm. The present findings clearly demonstrate that the integration of electron mediators with semiconductors is a feasible process for the design and development of efficient photochemical systems for CO₂ conversion.

A chemical system with enhanced efficiency for electron generation and transfer was constructed by the integration of TiO₂ hollow spheres with [Co(bipy)₃]²⁺.