Facile Synthesis of n-type (AgIn)(x)Zn(2(1-x))S2/p-type Ag2S Nanocomposite for Visible Light Photocatalytic Reduction To Detoxify Hexavalent Chromium

Applications of Fluorescent Carbon Dots as Photocatalysts: A Review

Carbon dots (CDs) have attracted considerable interest from the scientific community due to their exceptional properties, such as high photoluminescence, broadband absorption, low toxicity, water solubility and (photo)chemical stability. As a result, they have been applied in several fields, such as sensing, bioimaging, artificial lighting and catalysis. In particular, CDs may act as sole photocatalysts or as part of photocatalytic nanocomposites. This study aims to provide a comprehensive review on the use of CDs as sole photocatalysts in the areas of hydrogen production via water splitting, photodegradation of organic pollutants and photoreduction and metal removal from wastewaters. Furthermore, key limitations preventing a wider use of CDs as photocatalysts are pointed out. It is our hope that this review will serve as a basis on which researchers may find useful information to develop sustainable methodologies for the synthesis and use of photocatalytic CDs.

Introducing anthracene and amino groups into Ln-OFs for the photoreduction of Cr(vi) without additional photosensitizers or cocatalysts

The stable LCUH-100 was designed and synthesized, by incorporating chromophores into lanthanide MOFs, as a high-efficiency photocatalyst, which can rapidly and efficiently reduce Cr(vi) under visible-light irradiation and has good cycle stability.

One-pot preparation of multicomponent photocatalyst with (Zn, Co, Ni)(O, S)/Ga2O3 nanocomposites to significantly enhance hydrogen production

To enhance the production of hydrogen, multicomponent photocatalyst (Zn, Co, Ni)(O, S)/Ga2O3 nanocomposites were synthesized and optimized with different amounts of Ga precursor in a relatively low-temperature process.

Green rust functionalized geopolymer of composite cementitious materials and its application on treating chromate in a holistic system

Green rust functionalized geopolymer of composite cementitious materials (GR-CCM) was synthesized to improve the adsorption and subsequent stabilization/solidification of chromate in a holistic operating system. The initial pH in solution exhibited the most significant effect on the chromate removal by GR-CCM among three adsorption factors. The maximum monolayer adsorption capacity and theoretical saturation capacity of GR-CCM for Cr(VI) in the acidic condition were 55.01 mg/g and 41.70 mg/g, respectively. Amorphousness brought by loading GR weakened the crystallinity of composite cementitious materials (CCM), which enhanced the adsorption capacity of CCM and boosted the solidification process. The mixed-valent iron species in the GR-CCM not only directly engaged in the adsorption and reduction of chromate also positively strengthened the solidification of Cr species during the whole treatment. This study facilitates the application of GRs on the geopolymer materials and demonstrates the combination of adsorption and immobilization for the treatment of other potential heavy metal contamination.

Effective hydrogenation of carbonates to produce methanol over a ternary Cu/Zn/Al catalyst

Methanol synthesized from carbonate hydrogenation is of great importance for CO₂ utilization indirectly. Herein, a series of Cu/Zn/Al heterogeneous catalysts were prepared by co-precipitation with a synchronous aging step, and were applied for hydrogenation of diethyl carbonate (DEC) to produce methanol. Furthermore, the catalysts were characterized by physicochemical methods, such as N₂ adsorption, ICP-OES, N₂O titration, SEM, TEM, XRD, H₂-TPR and XPS in detail. Higher copper concentration led to a higher ratio of bulk CuOx species in the calcined samples, which resulted in different copper species distribution after the reduction process. Structure activity relationship analysis indicated that the balance of surface Cu⁰ and Cu⁺ species influenced the formation rate of methanol. A higher proportion of Cu⁺ to (Cu⁺ + Cu⁰) was conductive to methanol formation, while excessive Cu⁰ site density played a negative influence on the methanol synthesized from DEC. Cu/Zn/Al with a 45.2% weight fraction of copper showed better performance with a total methanol formation rate of 131.0 mg g_cat.⁻¹ h⁻¹. The reaction temperature and reaction time could obviously affect the reaction performance and the results suggested that 200 °C and 6 h were suitable. Furthermore, the long-term stability and activity of the catalyst was also studied on a fixed bed, and the yield of total methanol reached to 88.5% and the selectivity of total methanol gradually decreased to 74.0% within 200 h, which could be attributed to the detrimental influence derived from the increase of Cu⁰. The reaction pathways involved in the hydrogenation of DEC process were proposed. The substance scope was also extended to other carbonates and the catalyst exhibited superior catalytic performance toward linear carbonates. This work provided insights into carbonate hydrogenation over an effective Cu/Zn/Al catalyst, which could be utilized into upgrading CO₂ indirectly to produce commodity methanol under relatively mild reaction conditions.

The valence distribution of copper species in ternary Cu/Zn/Al catalysts have significant influence on diethyl carbonate hydrogenation to produce methanol.

Surface-passivated, soluble and non-toxic graphene nano-sheets for the selective sensing of toxic Cr(vi) and Hg(ii) metal ions and as a blue fluorescent ink

Non-toxic amine-functionalized soluble graphene nano-sheets (f-GNS) were synthesized by using an old and well-known simple organic procedure. The f-GNS exhibited enhanced optical properties, such as strong blue fluorescence emission with a high value of quantum yield (∼13%). The O,O'-bis-(2-aminopropyl) polypropylene glycol-block-polyethylene glycol-block-polypropylene glycol 800 as block polymeric amine (BPA)-passivized surface of f-GNS exhibited high aqueous solubility and excitation-dependent fluorescence emission behavior with a strong photo-stability performance. These f-GNS were tested for the significant selective sensing of toxic metal ions Cr(vi) and Hg(ii) from various tested toxic metal ions. The sensing experiment was supported by cyclic voltammetry analysis. The dual metal ion sensing method based on fluorescence showed the limit of detection (LOD) of ∼56 nM for Cr(vi) and ∼45 nM for Hg(ii) through a fluorescence quenching process. f-GNS were found to be non-toxic when tested over Escherichia coli (E.coli) cells. Additionally, the strong blue emission properties of f-GNS enabled their use as a suitable blue fluorescent ink under UV light illumination.

Full-color-emitting (CuInS2)ZnS-alloyed core/shell quantum dots with trimethoxysilyl end-capped ligands soluble in an ionic liquid

Zinc-copper-indium sulfide (ZCIS)-alloyed quantum dots are emerging as a new family of low toxic I-III-VI semiconductors due to their broad and color-tunable emissions as well as large Stokes shifts. Here, we fabricated a series of ZCIS QDs with tunable PL wavelengths and band-gap energies via a facile strategy by varying the ratio of A1-3 stock (Cu+/In3+) to the B stock (Zn2+) content. The ZnS shell was formed to improve the PL emission efficiency of the core nanoparticles and the PL emission wavelength of the resulting ZCIS/ZnS NCs gradually blue-shifted with an increase in the number of shell layers, resulting in a wide range of emissions from 800 nm to 518 nm that can be tuned by the core compositions or shell layer numbers for ZCIS/ZnS. Finally, the long-chain ligands dodecanethiol/octadecylamine on the quantum dots' surface were efficiently replaced by (3-mercaptopropyl)trimethoxysilane, thus enabling their solubility in an ionic liquid, which was confirmed via GC-MS. It also benefited for the co-dissolution of the polymers and chemical binding with other materials through the reactive silanol group, which provide stable and well-distributed ZCIS/ZnS QDs composites or surface coating by the QDs.

Facile Preparation of CNT/Ag2S Nanocomposites with Improved Visible and NIR Light Photocatalytic Degradation Activity and Their Catalytic Mechanism

In this work, a series of carbon nanotubes (CNT)/Ag₂S hybrid nanocomposites were successfully prepared by a facile precipitation method. Transmission electron microscope (TEM) observation indicates that Ag₂S nanoparticles with an average particle size of ~25 nm are uniformly anchored on the surface of CNT. The photocatalytic activities of the CNT/Ag₂S nanocomposites were investigated toward the degradation of rhodamine B (RhB) under visible and near-infrared (NIR) light irradiation. It is shown that the nanocomposites exhibit obviously enhanced visible and NIR light photocatalytic activities compared with bare Ag₂S nanoparticles. Moreover, the recycling photocatalytic experiment demonstrates that the CNT/Ag₂S nanocomposites possess excellent photocatalytic stability. The photoelectrochemical and photoluminescence measurements reveal the efficient separation of photogenerated charges in the CNT/Ag₂S nanocomposites. This is the dominant reason behind the improvement of the photocatalytic activity. Based on active species trapping experiments, the possible photocatalytic mechanism of CNT/Ag₂S nanocomposites for dye degradation under visible and NIR light irradiation was proposed.

Photocatalytic and Photo-Fenton Catalytic Degradation Activities of Z-Scheme Ag₂S/BiFeO₃ Heterojunction Composites under Visible-Light Irradiation

Z-scheme Ag₂S/BiFeO₃ heterojunction composites were successfully prepared through a precipitation method. The morphology and microstructure characterization demonstrate that Ag₂S nanoparticles (30⁻50 nm) are well-decorated on the surfaces of polyhedral BiFeO₃ particles (500⁻800 nm) to form Ag₂S/BiFeO₃ heterojunctions. The photocatalytic and photo-Fenton catalytic activities of the as-derived Ag₂S/BiFeO₃ heterojunction composites were evaluated by the degradation of methyl orange (MO) under visible-light irradiation. The photocatalytic result indicates that the Ag₂S/BiFeO₃ composites exhibit much improved photocatalytic activities when compared with bare Ag₂S and BiFeO₃. The optimum composite sample was observed to be 15% Ag₂S/BiFeO₃ with an Ag₂S mass fraction of 15%. Furthermore, the addition of H₂O₂ can further enhance the dye degradation efficiency, which is due to the synergistic effects of photo- and Fenton catalysis. The results of photoelectrochemical and photoluminescence measurements suggest a greater separation of the photoexcited electron/hole pairs in the Ag₂S/BiFeO₃ composites. According to the active species trapping experiments, the photocatalytic and photo-Fenton catalytic mechanisms of the Ag₂S/BiFeO₃ composites were proposed and discussed.

Synthesis and characterization of La-doped Zn(O,S) photocatalyst for green chemical detoxification of 4-nitrophenol

La-doped Zn(O,S) nanoparticles (NPs) with different contents of lanthanum have been synthesized with a simple sol-gel method at low temperature (90 ℃) for 4-nitrophenol (4-NP) detoxification. The as-prepared catalysts were characterized with X-ray diffraction (XRD), scanning electron microscope (SEM), high resolution transmission electron microscope (HRTEM), photoluminescence (PL) and UV-vis absorbance spectroscopy, X-ray photoelectron spectroscopy (XPS), electrochemical impedance spectroscopy (EIS), and photoresponsivity. In this work, it is considered that the detoxification of 4-NP to 4-aminophenol (4-AP) without NaBH₄ by using photocatalytic method is a green chemical conversion. The experimental data showed 30 ppm toxic 4-NP had been totally converted to useful 4-aminophenol (4-AP) with lower toxicity in 2 h, which was confirmed with a specific peak shift as indicated with UV-vis absorbance spectra and high performance liquid chromatography (HPLC) measurement. The lower amount of evolved hydrogen from photocatalytic process on La-doped Zn(O,S) NPs in the presence of 4-NP confirmed the produced hydrogen was consumed as a reducing agent during the 4-NP-to-4-AP conversion. The photocatalytic detoxification of 4-NP to 4-AP had been demonstrated and an appropriate mechanism based on the experimental data had been proposed and elucidated in this work.

Ternary assembly of g-C3N4/graphene oxide sheets /BiFeO3 heterojunction with enhanced photoreduction of Cr(VI) under visible-light irradiation

A novel ternary composite of graphitic carbon nitride (g-C₃N₄)/graphene oxide (GO) sheets/BiFeO₃ (CNGB) with highly enhanced visible-light photocatalytic activity toward Cr(VI) photoreduction is prepared and characterized. The characterization and photocatalysis experiments corroborate its reasonable band gap, efficient charge separation and transfer, widened visible-light adsorption, easy solid-liquid separation, good stability and superior catalytic activity of CNGB. Three CNGB samples with different ratios of g-C₃N₄ and BiFeO₃ (CNGB-1, -2, -3 with 2:4, 3:3, and 4:2, respectively), though possessing different adsorption ability, eventually remove all Cr(VI) ions via photocatalysis within 90 min. The catalytic efficiency of the composite is the highest at pH 2; increases in pH decrease the catalytic ability. The inorganic anions such as SO₄^-, Cl^-, and NO₃^- only slightly affects the photocatalytic process. The matching of the band structure between BiFeO₃ and g-C₃N₄ generates efficient photogenerated electron migration from the conduction band of g-C₃N₄ to that of BiFeO₃, which is also facilitated by the electron bridging and collecting effects of GO, and holes transfer from the valence band of BiFeO₃ to that of g-C₃N₄, yielding the efficient separation of photogenerated electron-hole pairs and the subsequent enhancement of photocatalytic activity. The research provides a theoretical basis and technical support for the development of photocatalytic technologies for effective application in wastewater treatment and Cr-contaminated water restoration.

Construction of spindle structured CeO2 modified with rod-like attapulgite as a high-performance photocatalyst for CO2 reduction

In this study, a spindle structured CeO₂ photocatalyst modified with rod-like attapulgite (CeO₂/ATP) was successfully prepared by simple high temperature calcination.

Highly fluorescent, color tunable and magnetic quaternary Ag–In–Mn–Zn–S quantum dots

We report a simple and effective synthesis of Mn : AIZS quantum dots exhibiting color-tunable photoluminescence emission and magnetic properties.

Facile Preparation of Nano-Bi₂MoO₆/Diatomite Composite for Enhancing Photocatalytic Performance under Visible Light Irradiation

In this work, a new nano-Bi₂MoO₆/diatomite composite photocatalyst was successfully synthesized by a facile solvothermal method. Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and UV-vis diffuse reflection spectroscopy (DRS) were employed to investigate the morphology, crystal structure, and optical properties. It was shown that nanometer-scaled Bi₂MoO₆ crystals were well-deposited on the surface of Bi₂MoO₆/diatomite. The photocatalytic activity of the obtained samples was evaluated by the degradation of rhodamine B (RhB) under the visible light (λ > 420 nm) irradiation. Moreover, trapping experiments were performed to investigate the possible photocatalytic reaction mechanism. The results showed that the nano-Bi₂MoO₆/diatomite composite with the mass ratio of Bi₂MoO₆ to diatomaceous earth of 70% exhibited the highest activity, and the RhB degradation efficiency reached 97.6% within 60 min. The main active species were revealed to be h⁺ and•O²⁻. As a photocatalytic reactor, its recycling performance showed a good stability and reusability. This new composite photocatalyst material holds great promise in the engineering field for the environmental remediation.

A simple one-pot synthesis of a Zn(O,S)/Ga2O3 nanocomposite photocatalyst for hydrogen production and 4-nitrophenol reduction

Herein, we demonstrate the great photocatalytic hydrogen evolution of a noble metal-free Zn(O,S)/Ga₂O₃ heterojunction nanocomposite in ethanol solution and its application in 4-nitrophenol reduction.

Enhanced photocatalytic properties of ZnFe2O4-doped ZnIn2S4 heterostructure under visible light irradiation

ZnFe₂O₄-doped ZnIn₂S₄ heterostructure was fabricated and showed enhanced photocatalytic performance under visible light irradiation.