Low-temperature synthesis of CdS/TiO2 composite photocatalysts: Influence of synthetic procedure on photocatalytic activity under visible light

Enhanced photocatalytic degradation of Acid Blue dye using CdS/TiO2 nanocomposite

Photocatalytic degradation is essential for the successful removal of organic contaminants from wastewater, which is important for ecological and environmental safety. The advanced oxidation process of photocatalysis has become a hot topic in recent years for the remediation of water. Cadmium sulphide (CdS) nanostructures doped with Titanium oxide (CdS/TiO₂) nanocomposites has manufactured under ambient conditions using a simple and modified Chemical Precipitation technique. The nanocomposites crystal structure, thermal stability, recombination of photo-generated charge carriers, bandgap, surface morphology, particle size, molar ratio, and charge transfer properties are determined. The production of nanocomposites (CdS-TiO₂) and their efficient photocatalytic capabilities are observed. The goal of the experiment is to improve the photocatalytic efficiency of TiO₂ in the visible region by doping CdS nanocomposites. The results showed that as-prepared CdS-TiO₂ nanocomposites has exhibited the highest photocatalytic activity in the process of photocatalytic degradation of AB-29 dye, and its degradation efficiency is 84%. After 1 h 30 min of visible light irradiation, while CdS and TiO₂ showed only 68% and 09%, respectively. The observed decolorization rate of AB-29 is also higher in the case of CdS-TiO₂ photocatalyst ~ 5.8 × 10⁻⁴mol L⁻¹ min⁻¹) as compared to the reported decolorization rate of CdS ~ 4.5 × 10⁻⁴mol L⁻¹ min⁻¹ and TiO₂ ~ 0.67 × 10⁻⁴mol L⁻¹ min⁻¹. This increased photocatalytic effectiveness of CdS-TiO₂ has been accomplished by reduced charge carrier recombination as a result of improved charge separation and extension of TiO₂ in response to visible light.

A review of volatile organic compounds (VOCs) degradation by vacuum ultraviolet (VUV) catalytic oxidation

Volatile organic compounds (VOCs), one of the most important gaseous air pollutants, are getting more and more attention, and a lot of technologies have been studied and applied to eliminate VOCs emissions. Advanced oxidation processes (AOPs) are considered as one of the most promising techniques used for the degradation of VOCs. Vacuum ultraviolet (VUV) catalytic oxidation system is a typical composite AOPs system involving several processes such as VUV photodegradation, photocatalytic oxidation (PCO), ozone catalytic oxidation (OZCO) and their combinations. VUV based catalytic oxidation processes have been intensively studied for degrading VOCs. This review summarizes the recent studies on the use of VUV catalytic oxidation for degrading VOCs. All the processes involved in VUV catalytic oxidation and their combinations have been reviewed. Studies of VOCs degradation by VUV catalytic oxidation can be generally divided into two aspects: developments of catalysts and mechanistic studies. Principles of different processes, strategies of catalyst development and reaction mechanism are summarized in this review. Two directions of prospective future work were also proposed.

Photothermal effect and cytotoxicity of CuS nanoflowers deposited over folic acid conjugated nanographene oxide

Herein, we present the rational synthesis of a multimode photothermal agent, NGO-FA-CuS, for the advancement of photothermal therapy of cancer. The hierarchical architecture created in NGO-FA-CuS was attained by the covalent conjugation of folic acid (FA) to nanographene oxide (NGO) through amide bonding, followed by the hydrothermal deposition of CuS nanoflowers. In this approach, instead of mere mixing or deposition, FA was covalently bonded to NGO, which helped in retaining their intrinsic properties after binding and allowed to access them in the resulting hybrid nanostructure. In this specifically designed photothermal agent, NGO-FA-CuS, each component has an explicit task, i.e., NGO, FA and CuS act as the quencher, cancer cell-targeting moiety and photothermal transduction agent, respectively. Prior to the grafting of FA molecules and the deposition of CuS nanoflowers, sulfonic acid groups were introduced into NGO to provide stability under physiological conditions. Under irradiation using a 980 nm laser, NGO-FA-CuS was able to attain a temperature of 63.1 °C within 5 min, which is far beyond the survival temperature for cancer cells. Therefore, the resulting temperature recorded for NGO-FA-CuS was sufficient to induce hyperthermia in cancer cells to cause their death. When coming into contact with cancer cells, NGO-FA-CuS can cause a rapid increase in the temperature of their nucleus, destroy the genetic substances, and ultimately lead to exhaustive apoptosis under illumination using a near-infrared (NIR) laser. An excellent photothermal efficiency of 46.2% under illumination using a 980 nm laser and outstanding cytotoxicity against HeLa, SKOV3 and KB cells were attained with NGO-FA-CuS. Moreover, NGO-FA-CuS displays exceptional persistent photo-stability without photo-corrosiveness. The photothermal effect of NGO-FA-CuS was found to be dependent on its concentration and the power density of the laser source. It was found that its cytotoxicity toward cancer cells was enhanced with an increase in the concentration of NGO-FA-CuS and the incubation period.

Enhanced visible light-driven photocatalytic activity of reduced graphene oxide/cadmium sulfide composite: Methylparaben degradation mechanism and toxicity

Reduced graphene oxide/cadmium sulfide (RGOCdS) nanocomposite synthesized through solvothermal process was used for methylparaben (MeP) degradation. The crystallinity of the nanocomposite was ascertained through X-ray diffraction. High resolution transmission electron microscope (HRTEM) results proved the absence of any free particle beyond the catalyst surface ensuring the composite nature of the prepared material. The enhancement in the activity on doping with RGO was substantiated by diffuse reflectance spectroscopy (DRS-UV). It is evident from the photocatalytic degradation experiments that RGOCdS is more efficient than pure CdS. Maximum MeP degradation (100%) was achieved after 90 min of irradiation with 750 mg/L RGOCdS dosage at an acidic pH of 3, for an initial MeP concentration of 30 mg/L. The degradation mechanism substantiated through HPLC-MS/MS analysis showed the complete degradation of MeP without any residual intermediaries. The catalyst could be sustained and reused for up to 9 cycles of usage. Phytotoxicity and mycotoxicity results evidently ascertain the environmental implications of the photocatalyst material.

Magnetically Recoverable TiO2/SiO2/γ-Fe2O3/rGO Composite with Significantly Enhanced UV-Visible Light Photocatalytic Activity

In this paper, we report the preparation of a new composite (TiO₂/SiO₂/γ-Fe₂O₃/rGO) with a high photocatalytic efficiency. The properties of the composite were examined by different analyses, including X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM), photoluminescence (PL), UV-Visible light diffuse reflectance spectroscopy, Fourier transform infrared spectroscopy (FTIR), Raman, vibrating-sample magnetometer (VSM), and nitrogen gas physisorption (BET) studies. The photocatalytic efficiency of the proposed composite was evaluated by the degradation of methylene blue under UV and visible light, and the results were compared with titanium dioxide (TiO₂), where degradation increased from 30% to 84% and 4% to 66% under UV and visible light, respectively. The significant increase in photocatalytic activity may be explained by the higher adsorption of dye on the surface of the composite and the higher separation and transfer of charge carriers, which in turn promote active sites and photocatalytic efficiency.

Recent progress on the enhancement of photocatalytic properties of BiPO4 using π-conjugated materials

Semiconductor photocatalysis is regarded as most privileged solution for energy conversion and environmental application. Recently, photocatalysis methods using bismuth-based photocatalysts, such as BiPO₄, have been extensively investigated owing to their superior efficacy regarding organic pollutant degradation and their further mineralization into CO₂ and H₂O. It is well known that BiPO₄ monoclinic phase exhibited better photocatalytic performance compared to Degussa (Evonik) P25 TiO₂ in term of ultraviolet light driven organic pollutants degradation. However, its wide band gap, poor adsorptive performance and large size make BiPO₄ less active under visible light irradiation. However, extensive research works have been conducted in the past with the aim of improving visible light driven BiPO₄ activity by constructing a series of heterostructures, mainly coupled with π-conjugated architecture (e.g., conductive polymer, dye sensitization and carbonaceous materials). However, a critical review of modified BiPO₄ systems using π-conjugated materials has not been published to date. Therefore, this current review article was designed with the aim of presenting a brief current state-of-the-art towards synthesis methods of BiPO₄ in the first section, with an especial focuses onto its crystal-microstructure, optical and photocatalytic properties. Moreover, the most relevant strategies that have been employed to improve its photocatalytic activities are then addressed as the main part of this review. Finally, the last section presents ongoing challenges and perspectives for modified BiPO₄ systems using π-conjugated materials.

Optimizing the synthesis of SnO2/TiO2/RGO nanocomposites with excellent visible light photocatalytic and antibacterial activities

Multifunctional SnO₂/TiO₂/RGO nanocomposites with enhanced photocatalytic degradation and antibacterial activity have been successfully synthesized by a facile one-pot environmentally friendly green hydrothermal route using titanium tetrabutoxide (TBOT), Na₂SnO₃ and graphene oxide (GO) without reducing agents and any structure-directing agents. The results demonstrate that the reaction pH conditions play important roles in the control of the crystallographic phases of TiO₂ and SnO₂. In addition, the visible-light-active photocatalytic and antibacterial activities of the synthesized composites were measured for the degradation of rhodamine B (RhB) and the growth inhibition of the Gram-negative bacteria Escherichia coli (E. coli), which are strongly affected by the SnO₂ loading content, the crystal structure of TiO₂ and the appropriate addition of graphene. The superior photocatalytic and antibacterial activities of the nanocomposites were attributed to their great optical adsorption capability and excellent charge separation and transfer efficiency. This study may provide new insights into the fabrication of efficient visible-light-active SnO₂/TiO₂/RGO nanocomposites and expand their applications in the environmental remediation and water disinfection fields.

Eosin Y sensitized BiPO4 nanorods for bi-functionally enhanced visible-light-driven photocatalysis

Eosin Y sensitized BiPO₄ nanorods enhanced the degradation efficiency of MB and 2,4-DCP compared to pristine BiPO₄ by 46.7 and 10.5 fold with a 100% mineralization rate.

Ultrasound assisted synthesis of Bi2NbO5F/rectorite composite and its photocatalytic mechanism insights

Enhancing the adsorbability of the photocatalysts is an effective way to improve the photocatalytic performance. Herein, we firstly synthesized a novel Bi₂NbO₅F/rectorite (BF/R) composite photocatalyst with high adsorption capacity via the ultrasound assisted route. The X-ray photoelectron spectrometer (XPS) analysis has demonstrated that the Bi₂NbO₅F and rectorite were connected with each other by weak chemical bonds. The introduced rectorite in the composite provided rich adsorption active sites for the adsorption of rhodamine B (RhB). The catalytic activity of the BF/R catalyst was evaluated by degrading RhB (5 mg/L) under UV-light irradiation. The BF/R composite with 32% rectorite exhibited the best photocatalytic degradation efficiency for degrading RhB in aqueous solution, which was 6.6 times higher than that of the bare BF sample. The improved activity of the BF/R composite can be ascribed to its strong adsorbability and enhanced light absorption. More importantly, the BF/R catalyst still showed good stability and high activity for degrading RhB after four recycles. Lastly, a possible photocatalytic mechanism on the BF/R composite was proposed. This work would provide helpful insights into the synthesis of the clay combined with Bi-based adjustable structure materials via ultrasound method.

Photocatalytic Degradation of Tetracycline Hydrochloride via a CdS-TiO₂ Heterostructure Composite under Visible Light Irradiation

A photocatalytic active CdS-TiO₂ heterostructure composite was prepared by hydrothermal method and its morphology and properties were characterized. Results indicate that the CdS nanoparticles deposited on the surface of a TiO₂ nanoparticles, which was in anatase phase. The particle scale of both of the components reached approximately 15 nm. In comparison to pure TiO₂ (410 nm), the light absorption edge of the heterostructure composite was 550 nm, which could extend the light response from UV to the visible region. Under visible light irradiation, the degradation efficiency of tetracycline hydrochloride by the CdS-TiO₂ composite achieved 87.06%, significantly enhancing photocatalytic activity than the as-prepared pure TiO₂ and commercial TiO₂ (Degussa P25). This character is attributed to the synergetic effect of these two components in the absorption of visible light.

Multiple carrier-transfer pathways in a flower-like In2S3/CdIn2S4/In2O3 ternary heterostructure for enhanced photocatalytic hydrogen production

A novel flower-like In2S3/CdIn2S4/In2O3 (ICS) ternary heterostructure (HS) is rationally constructed for the first time by a series of carefully designed procedures. In2O3 nanoflakes are the main constituent units which assemble into a flower-like skeleton structure, and CdIn2S4 nanoparticles are in situ generated on the surface of In2O3 nanoflakes through the transformation of CdS quantum dots (QDs) while In2S3 nanoparticles are in situ produced at the region between CdIn2S4 nanoparticles and In2O3 nanoflakes resulting from a synchronous sulfuration procedure. As expected, the rationally designed ICS ternary HSs display significantly enhanced photocatalytic H2 production, especially ICS5 (sulfurized for 5 h) with the highest H2 evolution rate of 20.04 μmol h-1 (10 mg catalyst is used for photocatalytic reaction), which is 26.7 times and 2.6 times higher than that of pure In2O3 (0.75 μmol h-1) and In2S3/In2O3 binary HS (7.88 μmol h-1), respectively. The enhanced photocatalytic activity can be attributed to the multiple interfaces formed in the ICS HSs, including the CdIn2S4-In2O3 interface, the In2S3-In2O3 interface, and the CdIn2S4-In2O3-In2S3 interface, which construct multiple pathways for the transfer of photogenerated charge carriers, effectively promoting the photocatalytic hydrogen production.

Enhanced visible light driven photocatalytic activity of CdO–graphene oxide heterostructures for the degradation of organic pollutants

Synthesis of efficient CdO based photocatalysts for enhanced visible light driven photocatalytic degradation of organic pollutants mostly emphasize on (1) increase of surface area of the photocatalyst and (2) high charge separation and suppressed recombination of photogenerated electron–hole pairs.

BiVO4 quantum dot-decorated BiPO4 nanorods 0D/1D heterojunction for enhanced visible-light-driven photocatalysis

Herein, we report a BiVO₄ quantum dot (QDs)-decorated BiPO₄ nanorods 0D/1D heterojunction via an in situ growth method.

Fe2O3/BiOI-Based Photoanode with n-p Heterogeneous Structure for Photoelectric Conversion

We report a promising photoanode material of Fe₂O₃/BiOI for efficient photoelectric conversion in solar cells, which was fabricated with BiOI attached to a one-dimensional Fe₂O₃ nanorod array. The two semiconductors of p-type BiOI and n-type Fe₂O₃ formed a heterogeneous structure for efficient charge separation. The highest open circuit voltage and short circuit current of the solar cell can reach 0.41 V and 4.89 mA/cm², respectively. This study opens an available field to develop low-cost and environmentally friendly photoelectric materials for solar cells.

Visible light-assisted efficient degradation of dye pollutants with biomass-supported TiO2 hybrids

The objective of this work was to develop a novel organic-inorganic hybrid nanomaterial from agricultural biomass waste for environmental applications. The sugarcane bagasse (SB) supported TiO₂ hybrids were firstly synthesized via a sol-gel method. A series of characterizations were carried out to reveal the structures and components of obtained hybrids. Due to organic-inorganic hybrid (OIH) effect and element doping, the SB-TiO₂ hybrid can expand its optical absorbance ranging from ultraviolet to visible light. The optimal hybrid catalyst prepared with SB doping amount of 2g in 100mL titanic gel and calcined at 200°C was able to degradate 95.0% methyl orange (MO) in 5h under visible light. This study will pave a new and facile pathway for novel visible light driven photocatalysts based on TiO₂ modified by agricultural biomass waste.

CdS quantum dots confined in mesoporous TiO2 with exceptional photocatalytic performance for degradation of organic polutants

In this paper, the mesoporous TiO₂ with different concentration of CdS quantum dots (i.e., x% CdS/TiO₂) was successfully fabricated by the sol-gel method. The composition, structure and morphology of the nanocomposites were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), UV-vis diffuse reflectance spectroscopy (UV-Vis/DRS) and nitrogen physical adsorption test and so on. The proportion of CdS and TiO₂ is very important for the photocatalytic performance. As a result, the photocatalytic degradation performance from the most to the least is in the order of 2% CdS/TiO₂, 4% CdS/TiO₂, 8% CdS/TiO₂, pure TiO₂ and 1% CdS/TiO₂. The photocatalytic (PC) activity of the 2% CdSTiO₂ is characterized by photocatalytic degradation of methyl orange, which can be completely degraded within 45 min better than 60 min TiO₂ takes. It is also much better than CdS. Moreover, other four organic pollutants, such as methylthionine chloride, bisphenol A, rhodamine B, malachite green can also be degraded quickly on the condition of 2% CdS/TiO₂. What's more, the chemical stability and cycling capability of 2% CdS/TiO₂ are reflected by five cyclic degradation of methyl orange.

Enhanced Photocatalytic Activity of CdS-Decorated TiO₂/Carbon Core-Shell Microspheres Derived from Microcrystalline Cellulose

The fabrication of reusable and biodegradation materials from renewable resources such as cellulose is essential for a sustainable world. The core-shell structured CdS-decorated TiO₂/Carbon microspheres (CdS/TiO₂/Carbon MS) photocatalyst was synthesized with controlled hydrolysis and a novel sonochemical method. It was prepared by using crosslinked microcrystalline cellulose as the core, tetrabutyl titanate as the titania source and CdS as the photosensitizer. The morphology, chemical structure and properties of the obtained material were characterized by many means. Additionally, the photocatalytic activity of the CdS/TiO₂/Carbon MS was evaluated by the photodegradation efficiency of Rhodamine B solution, which reached 95.24% under visible light irradiation. This study demonstrated the excellent photocatalytic performance of CdS/TiO₂/Carbon MS, which might have promising applications in environmental treatments.

Self-Generated Macrochannel-Structure TiO2/g-C3N4 with High Photocatalytic Activity

TiO2/g-C3N4 composites with macrochannel structure were successfully synthesised without using templates by the simple dropwise addition of tetrabutyl titanate containing graphitic carbon nitride (g-C3N4) to a water-ethanol mixed solution, which was then calcined at 400°C. The as-prepared samples were characterised by X-ray diffraction, scanning electron microscopy, and UV-visible absorption spectroscopy. The photocatalytic activities of the samples were evaluated by the photocatalytic degradation of methyl orange in an aqueous medium under visible-light and simulated sunlight irradiation. The results show that the g-C3N4 content in TiO2/g-C3N4 composites plays an important role in the formation of macrochannels. Only samples containing less than 10 wt-% of g-C3N4 exhibit macrochannel structure. TiO2/g-C3N4 composites with macrochannel structure displayed enhanced photocatalytic activity. G-C3N4 content exhibited an obvious influence on photocatalytic performance, and the optimal loading of g-C3N4 was 10 wt-%. The enhanced photocatalytic activity could be attributed to the synergetic effects of the macrochannel structure, the large specific surface area, and the heterojunction between TiO2 and g-C3N4. The main oxidative species responsible for the photodegradation of pollutants were further confirmed by the trapping experiments.

Facile room-temperature synthesis of carboxylated graphene oxide-copper sulfide nanocomposite with high photodegradation and disinfection activities under solar light irradiation

Carboxylic acid functionalized graphene oxide-copper (II) sulfide nanoparticle composite (GO-COOH-CuS) was prepared from carboxylated graphene oxide and copper precursor in dimethyl sulfoxide (DMSO) by a facile synthesis process at room temperature. The high-effective combination, the interaction between GO-COOH sheets and CuS nanoparticles, and the enhanced visible light absorption were confirmed by transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermo gravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), UV-vis diffuse reflectance spectra (DRS) and Photoluminescence (PL) spectra. The as-synthesized GO-COOH-CuS nanocomposite exhibited excellent photocatalytic degradation performance of phenol and rhodamine B, high antibacterial activity toward E. coli and B. subtilis, and good recovery and reusability. The influence of CuS content, the synergistic reaction between CuS and GO-COOH, and the charge-transfer mechanism were systematically investigated. The facile and low-energy synthesis process combined with the excellent degradation and antibacterial performance signify that the GO-COOH-CuS has a great potential for water treatment application.

Green synthesis of Y2O3:Dy(3+) nanophosphor with enhanced photocatalytic activity

Facile and green route was employed for the synthesis of Y2O3:Dy(3+) (1-11 mol%) nanostructures (NSs) using Aloe vera gel as fuel. The formation of different morphologies of Y2O3:Dy(3+) NSs were characterized by SEM, TEM and HRTEM. PXRD data and Rietveld analysis evident the formation of single phase Y2O3 with cubic crystal structure. The influence of Dy(3+) ion concentration on the structure morphology, UV absorption, PL emission and photocatalytic activity of NSs were investigated. NSs exhibited an intense warm white emission with CIE chromaticity coordinates (0.32, 0.33) and average CCT value ∼5525 K which corresponds to vertical day light. The control of Dy(3+) ion on Y2O3 matrix influences the photocatalytic decolorization of Metanil Yellow as a model compound was evaluated. The enhanced photocatalytic activities of core shell structured Y2O3:Dy(3+) (1 mol%) was attributed to co-operation effect of dopant concentration, crystallite size, textural properties and capability for reducing electron-hole pair recombination. Further, the recycling catalytic ability of Y2O3:Dy(3+) (1 mol%) nanostructure was also evaluated and found promising photocatalytic performance with negligible decrease in decolorization efficiency even after sixth successive cyclic runs. Considering its green, facile synthesis and recyclable feature from an aqueous solution, the present Y2O3:Dy(3+) (1 mol%) nanophosphor can be considered as one of the ideal photocatalyst for various potential applications.

Bio-inspired synthesis of Y2O3: Eu(3+) red nanophosphor for eco-friendly photocatalysis

We report the synthesis of Y2O3: Eu(3+) (1-11 mol%) nanoparticles (NPs) with different morphologies via eco-friendly, inexpensive and simple low temperature solution combustion method using Aloe Vera gel as fuel. The formation of different morphologies of Y2O3: Eu(3+) NPs were characterized by PXRD, SEM, TEM, HRTEM, UV-Visible and PL techniques. The PXRD data and Rietveld analysis confirms the formation of single phase Y2O3 with cubic crystal structure. The influence of Eu(3+) ion concentration on the morphology, UV-Visible absorption, PL emission and photocatalytic activity of Y2O3: Eu(3+) nanostructures were investigated. Y2O3: Eu(3+) NPs exhibit intense red emission with CIE chromaticity coordinates (0.50, 0.47) and correlated color temperature values at different excitation ranges from 1868 to 2600 K. The control of Eu(3+) ion on Y2O3 matrix influences the photocatalytic decolorization of methylene blue (MB) as a model compound was evaluated under UVA light. Enhanced photocatalytic activity of conical shaped Y2O3: Eu(3+) (1 mol%) was attributed to dopant concentration, crystallite size, textural properties and capability of reducing the electron-hole pair recombination. The trend of inhibitory effect in the presence of different radical scavengers followed the order SO4(2-)>Cl(-)>C2H5OH>HCO3(-)>CO3(2-). These findings show great promise of Y2O3: Eu(3+) NPs as a red phosphor in warm white LEDs as well as eco-friendly heterogeneous photocatalysis.

Carbon-doped titania nanoplates with exposed {001} facets: facile synthesis, characterization and visible-light photocatalytic performance

C-doped TiO₂ nanoplates (CTNP) with exposed {001} facets were synthesized for the first time. The obtained CTNP presented high visible-light photocatalytic activity. A reasonable mechanism of photocatalysis on CTNP under visible light was proposed.

Review on modified N–TiO2 for green energy applications under UV/visible light: selected results and reaction mechanisms

Modifications of the activity, band structure, morphology, optical and electronic properties of N–TiO₂ for energy and environmental applications.

Photocatalytic reduction of o-chloronitrobenzene under visible light irradiation over CdS quantum dot sensitized TiO2

CdS QDs-P25 was prepared by tethering CdS QDs with P25 through l-cysteine, and exhibited excellent photocatalytic activity under visible light. The photocatalytic reduction mechanism over CdS QDs-P25 was found to be a hydrogen transfer process between o-CNB and HCOOH molecules.