Ni-doped and Ni/Cr co-doped TiO2 nanotubes for enhancement of photocatalytic degradation of methylene blue

Recent progress in defect-engineered metal oxides for photocatalytic environmental remediation

Rapid industrial advancement over the last few decades has led to an alarming increase in pollution levels in the ecosystem. Among the primary pollutants, harmful organic dyes and pharmaceutical drugs are directly released by industries into the water bodies which serves as a major cause of environmental deterioration. This warns of a severe need to find some sustainable strategies to overcome these increasing levels of water pollution and eliminate the pollutants before being exposed to the environment. Photocatalysis is a well-established strategy in the field of pollutant degradation and various metal oxides have been proven to exhibit excellent physicochemical properties which makes them a potential candidate for environmental remediation. Further, with the aim of rapid industrialization of photocatalytic pollutant degradation technology, constant efforts have been made to increase the photocatalytic activity of various metal oxides. One such strategy is the introduction of defects into the lattice of the parent catalyst through doping or vacancy which plays a major role in enhancing the catalytic activity and achieving excellent degradation rates. This review provides a comprehensive analysis of defects and their role in altering the photocatalytic activity of the material. Various defect-rich metal oxides like binary oxides, perovskite oxides, and spinel oxides have been summarized for their application in pollutant degradation. Finally, a summary of existing research, followed by the existing challenges along with the potential countermeasures has been provided to pave a path for the future studies and industrialization of this promising field.

Round-the-Clock Adsorption-Degradation of Tetracycline Hydrochloride by Ag/Ni-TiO2

The synergy of adsorption and photocatalysis is a good method to remove organic pollutants in wastewater. In recent decades, persistent photocatalysis has gained considerable interest for its ability to sustain the catalytic degradation of organic pollutants in the dark. Herein, we report three different TiO2 nanomaterials to remove tetracycline hydrochloride (TCH) in solution. We found that the removal ability of TiO2, Ni-TiO2, and Ag/Ni-TiO2 is 8.8 mg/g, 13.9 mg/g and 23.4 mg/g, respectively, when the initial concentration of TCH is 50 mg/L. Chemical adsorption could be the rate-determining step in the TCH adsorption process. Moreover, Ag nanoparticles dispersed on Ni doped TiO2 surface act as traps to capture photo-generated electrons upon illumination with indoor light. The holes in Ag/Ni-TiO2 serve as critical oxidative species in TCH degradation under dark conditions. This work provides new insights into the design of persistent photocatalysts that can be activated by weak illumination and degrade organic pollutants in wastewater after sunset.

Dual-defect semiconductor photocatalysts for solar-to-chemical conversion: advances and challenges

Among the renewable energy technologies to deal with increasing energy crisis and environmental concerns, solar-to-chemical conversion via photocatalysis holds great promise for sustainable energy supply. To date, a variety of modification strategies with different types of semiconducting materials have been proposed to boost photocatalytic efficiency. Recently, dual-defect semiconductor photocatalysts have emerged as an advantageous candidate with superior performance in improving photocatalytic activity compared to their defect-free or single-defect counterparts. In this review, focus is laid on the advances of dual-defect semiconductor photocatalysts for energy photocatalysis. Possible schemes for two different defects within a single semiconductor are firstly sorted based on the types of defects, and synthesis strategies to achieve various defect schemes as well as techniques to characterize different defects are then introduced. In particular, the effect of different defects on photocatalytic performance is emphasized, and the advances in dual-defect semiconductors for solar-to-chemical conversions are summarized based on different defect schemes. Finally, the future challenges and opportunities of dual-defect semiconductors for photocatalysis are discussed. This article is expected to provide an overall insight into existing dual-defect semiconductor photocatalysts and inspire the development of new defect-rich materials for photocatalytic energy production.

Phytoassisted synthesis of CuO and Ag-CuO nanocomposite, characterization, chemical sensing of ammonia, degradation of methylene blue

The elimination of hazardous industrial pollutants from aqueous solutions is an emerging area of scientific research and a worldwide problem. An efficient catalyst, Ag-CuO was synthesized for the degradation of methylene blue, the chemical sensing of ammonia. A simple novel synthetic method was reported in which new plant material Capparis decidua was used for the reduction and stabilization of the synthesized nanocatalyst. A Varying amount of Ag was doped into CuO to optimize the best catalyst that met the required objectives. Through this, the Ag-CuO nanocomposite was characterized by XRD, SEM, HR-TEM, EDX, and FTIR techniques. The mechanism of increased catalytic activity with Ag doping involves the formation of charge sink and suppression of drop back probability of charge from conduction to valance band. Herein, 2.7 mol % Ag-CuO exhibited better catalytic activities and it was used through subsequent catalytic experiments. The experimental conditions such as pH, catalyst dose, analyte initial concentration, and contact time were optimized. The as-synthesized nanocomposite demonstrates an excellent degradation efficacy of MB which is 97% at pH 9. More interestingly, the as-synthesized catalyst was successfully applied for the chemical sensing of ammonia even at very low concentrations. The lower limit of detection (LLOD) also called analytic sensitivity was calculated for ammonia sensing and found to be 1.37 ppm.

Microfluidic Fabrication of Monodisperse and Recyclable TiO2-Poly(ethylene glycol) Diacrylate Hybrid Microgels for Removal of Methylene Blue from Aqueous Medium

Nearly monodisperse titanium oxide-polyethylene glycol diacrylate [TiO2-P(EGDA)] hybrid microbeads containing 0.5 wt % TiO2 nanoparticles entrapped within a P(EGDA) cross-linked polymeric network were synthesized using a modular Lego-inspired glass capillary microfluidic device. TiO2-P(EGDA) hybrid microgels were characterized by optical microscopy, scanning electron microscopy, X-ray diffraction, energy dispersive X-ray spectroscopy, and thermogravimetric analysis. The fabricated TiO2-P(EGDA) hybrid microgel system showed 100% removal efficiency of methylene blue (MB) from its 1-3 ppm aqueous solutions after 4 h of UV light irradiation at 0.2 mW/cm2 at the loading of 25 g/L photocatalyst beads in the reaction mixture, corresponding to the loading of naked TiO2 of just 0.025 g/L. No decrease in photocatalytic efficiency was observed in 10 repeated runs with recycled photocatalyst using a fresh 1 ppm MB solution in each cycle. The rate of photocatalytic degradation was controlled by the UV light irradiance, catalyst loading, and the initial dye concentration. Physical adsorption of MB onto the surface of composite microgel was also observed. The adsorption data was best fitted with the Langmuir adsorption isotherm and the Elovich kinetic model. TiO2-P(EGDA) microgel beads are biocompatible, can be prepared with a tunable size in the microfluidic device, and can easily be separated from the reaction mixture by gravity settling. The TiO2-P(EGDA) system can be used for the removal of other toxic dyes and micropollutants from industrial wastewater.

Ba2-xHoxSr2-yNiyFe12O22 and its composite with MXene: synthesis, characterization and enhanced visible light mediated photocatalytic activity for colored dye and pesticide

The rapid recombination of charges of photogenerated electrons and holes severely limits single semiconductor photocatalytic applications. In this study, a simple and facile sol-gel approach was used to synthesize Ba2-xHoxSr2-yNiyFe12O22 (x = 0, 0.1 and y = 0, 0.5). The composite of holmium-nickel doped barium-strontium ferrite with MXene (Ba1.9Ho0.1Sr1.5Ni0.5Fe12O22@MXene) was synthesized by ultrasonication method. These synthesized samples were subsequently used to photodegrade rhodamine B (RhB) and pendimethalin under visible light illumination. The results of the experiments demonstrated that MXene, as a cocatalyst, considerably reduces the rate of recombination of charges and broadens absorption of visible light by providing increased surface functional groups to improve the photocatalytic activity of synthesized samples. MXene is thermally stable, have high electrical conductivity, have adjustable bandgap, and hydrophilic in nature. The optimized Ba1.9Ho0.1Sr1.5Ni0.5Fe12O22@MXene composite demonstrated an excellent photocatalytic rate by degrading 78.88% RhB and 75.59% pendimethalin in 140 minutes. Moreover, the scavenging experiment revealed that photogenerated electrons and holes were the primary active species involved in RhB and pendimethalin photodegradation, respectively. Ba1.9Ho0.1Sr1.5Ni0.5Fe12O22@MXene showed increased photocatalytic behavior because it has increased surface area which decreases rate of recombination of electron and hole pair, hence photocatalytic activity increases. It is observed that Ba1.9Ho0.1Sr1.5Ni0.5Fe12O22@MXene has potential application in photocatalytic degradation of harmful pollutants.

An emerging expanse: Novel and eco-friendly-biogenic synthesis of E. cardamomum-wrapped TiO2 nanoparticles for environmental and biological applications

The present research is targeted at E. cardamomum-derived TiO2-photocatalyst synthesis, reporting for the first time. The structural properties observed from the XRD pattern reveal that EC:TiO2 has an anatase phase and crystallite size is assessed by Debye-Scherrer's method (3.56 nm), WH-method (3.30 nm), and Modified-Debye-Scherrer's method (3.27 nm). An optical study by the UV-Vis spectrum shows strong absorption at 313 nm, and the corresponding band gap value is 3.28 eV. The topographical and morphological properties revealed by SEM and HRTEM images, elucidate the formation of multi-shaped particles of nano-size. Further, the phytochemicals on the EC:TiO2 NPs' surface are confirmed by the FTIR spectrum. The photocatalytic activity is well studied under UV light towards Congo Red dye, along with an effect of the dose of catalyst. EC:TiO2 (20 mg) has exhibited high photocatalytic efficiency up to 97% for 150 min of exposure due to the morphological, structural, and optical properties. CR degradation reaction exhibits pseudo-first-order kinetics, displaying a rate constant value of 0.01320 min-1. Reusability investigations reveal that after four photocatalysis cycles, EC:TiO2 has an effective efficiency of >85%. Additionally, EC:TiO2 NPs have been assessed for antibacterial activity and show potential against two bacterial species (S. aureus and P. aeruginosa). Therefore, these research outcomes from the eco-friendly and low-cost synthesis, are promising for the use of EC:TiO2 as a talented photocatalyst towards the removal of crystal violet dye as well as an antibacterial agent against bacterial pathogens.

Organic waste peel-assisted synthesis of ZnSe nanoparticles for solar-driven photocatalytic degradation of cationic and anionic dye

The environment and public health are currently being threatened by the water pollution caused by dyes. Finding eco-friendly and economically viable photocatalysts has been a hot issue in recent years, as photocatalytic dye degradation is essential for eliminating dye from contaminated water as compared to other methods because of the cost factor and efficiency in removing organic contaminants. Using un-doped ZnSe for degrading activity has very seldom been attempted up to this point. Therefore, the current research focuses on the use of zinc selenide nanomaterials, which are produced via a green synthesis process from the organic waste peels of orange and potato using the hydrothermal method, and utilizes them as photocatalysts for the degradation of dyes using sunlight as a natural source of light. The crystal structure, bandgap, and surface morphology and analysis of the synthesized materials serve as indicators of their characteristics. Citrate in orange peel-mediated synthesis assists in forming a particle size of 1.85 nm and a large surface area of 17.078 m2/g enabling more surface-active sites resulting in degradation efficiency of 97.16% and 93.61% for methylene blue and Congo red dye, respectively, which outperforms commercial ZnSe in the dye degradation. The presented work maintains overall sustainability in real-practical applications by utilizing sunlight in photocatalytic degradation activity instead of sophisticated equipment and using waste peels as a capping and stabilizing agent in the green synthesis method for the preparation of photocatalysts.

Experimental Studies on TiO2 NT with Metal Dopants through Co-Precipitation, Sol-Gel, Hydrothermal Scheme and Corresponding Computational Molecular Evaluations

In the last decade, TiO₂ nanotubes have attracted the attention of the scientific community and industry due to their exceptional photocatalytic properties, opening a wide range of additional applications in the fields of renewable energy, sensors, supercapacitors, and the pharmaceutical industry. However, their use is limited because their band gap is tied to the visible light spectrum. Therefore, it is essential to dope them with metals to extend their physicochemical advantages. In this review, we provide a brief overview of the preparation of metal-doped TiO₂ nanotubes. We address hydrothermal and alteration methods that have been used to study the effects of different metal dopants on the structural, morphological, and optoelectrical properties of anatase and rutile nanotubes. The progress of DFT studies on the metal doping of TiO₂ nanoparticles is discussed. In addition, the traditional models and their confirmation of the results of the experiment with TiO₂ nanotubes are reviewed, as well as the use of TNT in various applications and the future prospects for its development in other fields. We focus on the comprehensive analysis and practical significance of the development of TiO₂ hybrid materials and the need for a better understanding of the structural-chemical properties of anatase TiO₂ nanotubes with metal doping for ion storage devices such as batteries.

Photocatalytic Degradation of Methyl Orange and Methylene Blue Dyes by Engineering the Surface Nano-Textures of TiO2 Thin Films Deposited at Different Temperatures via MOCVD

TiO₂ thin films were deposited on quartz substrates by metal-organic chemical vapor deposition (MOCVD) at temperatures of 250, 350, and 450 °C. X-ray diffraction (XRD) data revealed the production of a pure anatase phase, a decrease in crystallite size, and a textural change as deposition temperature increased. Atomic force microscopy (AFM) was used to study the morphological properties and confirm XRD results. UV-Vis.-NIR spectroscopy was used to investigate the optical properties of the samples. The effect of deposition temperature on wettability was investigated using contact angle measurements. Sunlight photocatalytic properties increased with the increase in deposition temperature for methyl orange and methylene blue. Films were post-annealed at 500 °C for 2 h. The effect of annealing on all the above-mentioned properties was explored. The kinetic analysis demonstrated superb agreement with the kinetic pseudo-first-order model. The rate of photocatalytic degradation of MB was ~8, 13, and 12 times that of MO using 250, 350, and 450 °C deposited films, respectively. Photodegradation was found to depend on the specific surface area, type of pollutant, and annealing temperature.

Photocatalytic activity of visible-light-driven L-Proline-TiO2/BiOBr nanostructured materials for dyes degradation: The role of generated reactive species

L-Proline (2%)-TiO₂/BiOBr (30%) nanocomposite was synthesized to obtain high photocatalytic performance in the visible light region and infrared radiation(IR) for methylene blue (MB) and congo red (CR) removal from the contaminated wastewater. L-Proline (2%)-TiO₂/BiOBr (30%) photocatalyst with strong absorption near IR wavelength and high charge separation ability was fabricated for the first time. X-ray diffraction (XRD), Fourier transform infrared (FTIR), field-emission scanning electron microscope (FESEM)/Energy Dispersive X-ray (EDX), UV-Vis diffuse reflectance spectrum (DRS), photoluminescence (PL) and Brunauer-Emmett-Teller (BET) characterization techniques show that the visible driven nanocomposite was successfully synthesized. According to the UV-DRS analysis, the estimated band gaps for the L-proline (2%)-TiO₂ and L-Proline (2%)-TiO₂/BiOBr (30%) nanostructures were respectively 2.3 eV and 2.1 eV.The nanoparticles exhibited enhanced photocatalytic activity (93-100%) and high mineralization efficiency (71-89% TOC removal) for both the dyes. The best photocatalytic activity was achieved by adding 2 wt% of L-Proline and 30 wt% of BiOBr into TiO₂ sol. Response surface methodology (RSM) was employed to find significant parameters and their optimum values for maximum degradation, which show pH, dye concentration, irradiation time, and catalyst dosage for both the dyes are significant. The best photocatalytic degradation efficiency was achieved at the optimum conditions of pH = 7.7, catalyst dosage = 0.71 g/L, irradiation time = 142 and dye concentration = 11 mg/L for MB. Scavenger study showed that •OH radicals are responsible for the degradation process.

Fabrication of Ni/TiO2 visible light responsive photocatalyst for decomposition of oxytetracycline

Nickel-impregnated TiO₂ photocatalyst (NiTP) responding to visible light was prepared by the liquid phase plasma (LPP) method, and its photoactivity was evaluated in degrading an antibiotic (oxytetracycline, OTC). For preparing the photocatalyst, nickel was uniformly impregnated onto TiO₂ (P-25) powder, and the nickel content increased as the number of LPP reactions increased. In addition, the morphology and lattice of NiTP were observed through various instrumental analyses, and it was confirmed that NiO-type nanoparticles were impregnated in NiTP. Fundamentally, as the amount of impregnated nickel in the TiO₂ powder increased sufficiently, the band gap energy of TiO₂ decreased, and eventually, the NiTP excited by visible light was synthesized. Further, OTC had a decomposition reaction pathway in which active radicals generated in OTC photocatalytic reaction under NiTP were finally mineralized through reactions such as decarboxamidation, hydration, deamination, demethylation, and dehydroxylation. In effect, we succeeded in synthesizing a photocatalyst useable under visible light by performing only the LPP single process and developed a new advanced oxidation process (AOP) that can remove toxic antibiotics.

Photocatalytic Degradation of Organic Dyes Contaminated Aqueous Solution Using Binary CdTiO2 and Ternary NiCdTiO2 Nanocomposites

The synergistic effect of binary CdTiO2 and ternary NiCdTiO2 on the photocatalytic efficiency of TiO2 nanoparticles was investigated. The SEM analysis demonstrates spherical TiO2 NPs of different sizes present in agglomerated form. The structural analysis of the nanocomposites reveals a porous structure for TiO2 with well deposited Cd and Ni NPs. TEM images show NiCdTiO2 nanocomposites as highly crystalline particles having spherical and cubical geometry with an average particle size of 20 nm. The EDX and XRD analysis confirm the purity and anatase phase of TiO2, respectively. Physical features of NiCdTiO2 nanocomposite were determined via BET analysis which shows that the surface area, pore size and pore volume are 61.2 m2/g, 10.6 nm and 0.1 cm3/g, respectively. The absorbance wavelengths of the CdTiO2 and NiCdTiO2 nanocomposites have shown red shift as compared to the neat TiO2 due to coupling with Ni and Cd that results in the enhanced photocatalytic activity. The photocatalytic activity demonstrated that TiO2, CdTiO2 and NiCdTiO2 degrade methylene blue (MB) and methyl green (MG) about 76.59, 82, 86% and 63.5, 88, 97.5%, respectively, at optimum reaction conditions.

Activated carbon derived from sugarcane and modified with natural zeolite for efficient adsorption of methylene blue dye: experimentally and theoretically approaches

The introduction of activated carbon/natural zeolite (AC/NZ) as an efficient and reliable nanoadsorbent for enhancing methylene blue (MB) dye adsorption. By calcining sugarcane waste at various temperatures between 500 and 900 °C, activated carbons (ACs) are formed. Both XRD and SEM were used for the characterization of the prepared adsorbents. Adsorption measurements for the removal of MB dye were made on the impact of pH, beginning MB concentration, and contact time. The maximum AC500/NZ adsorption capacity for MB dye at 25 °C, pH 7, and an AC500/NZ mass of 50 mg was found to be approximately 51 mg/g at an initial concentration of 30 ppm. The pseudo-second-order kinetics model and the Temkin isotherm model describe the adsorption process. The Temkin model shows that the adsorption energy is 1.0 kcal/mol, indicating that the MB-to-AC500/NZ adsorption process occurs physically. Our Monte Carlo (MC) simulation studies supported our findings and showed that the Van der Waals dispersion force was responsible for the MB molecule's physical adsorption. The AC500/NZ adsorbent is thought to be a strong contender for water remediation.

Enhanced Photocatalytic Activity of Anatase/Rutile Heterojunctions by Lanthanum and Tin Co-Doping

Anatase/rutile heterojunctions were prepared using the sol-gel method and modified by La/Sn single doping and co-doping. Sn doping promoted the transformation from anatase to rutile, while La doping inhibited the phase transformation. La and Sn co-doping showed an inhibitory effect. The co-doping of La and Sn did not increase visible-light absorption, but exhibited a synergistic effect on inhibiting the recombination of photogenerated electrons and holes, which improved the photocatalytic activity on the basis of single-element modification. The first-order reaction rate constant of La/Sn co-doped sample was 0.027 min-1, which is 1.8 times higher than that of pure TiO2 (0.015 min-1). Meanwhile, the mechanism of photodegradation of methylene blue (MB) by La/Sn co-doped anatase/rutile heterojunctions was discussed through electrochemical measurements and free-radical trapping experiments.

Improved photodegradation of antibiotics pollutants in wastewaters by advanced oxidation process based on Ni-doped TiO2

The number of antibiotic compounds in wastewaters has been growing globally due to the covid-19 problem. Using antibiotics to treat the patients would produce larger amounts of these compounds into the environment with negative impacts. Hence, finding out the method for the elimination of toxic organic pollutants as well as antibiotics in water is urgent (In this study, the treatment of antibiotic pollutants including cefalexin (CF) and tetracycline (TC) was investigated by applying the advanced oxidation process based on Ni-doped TiO₂ (Ni-TiO₂). The characterizations technologies such as XRD, XPS, UV-vis, PL, and PC indicated that Ni doping would improve the photocatalytic performance of TiO₂. In the photodegradation experiments, the Ni-TiO₂ possessed high photocatalytic degradation efficiencies with 93.6% for CF and 82.5% for TC. Besides, the removal rates of antibiotics after five cycles are higher than 75%, implying excellent stability of Ni-TiO₂ photocatalyst. The result from the treatment of wastewater samples revealed that the Ni-TiO₂ photocatalytic had good performance for removal of CF and TC at a high level of 88.6 and 80.2%, respectively.

Efficient photocatalytic degradation of nitrobenzene by copper-doped TiO2: kinetic study, degradation pathway, and mechanism

Cu-doped TiO2 (0.1, 0.25, and 0.5% Cu-TiO2) photocatalyst was prepared by sol-gel method and was characterized by powder XRD, FTIR, TEM, SEM, EDX, UV-vis diffuse reflectance (DRS), photoluminescence (PL), and Raman spectroscopy. The XRD spectrum shows tetragonal anatase phase. TEM analysis indicate that the nanoparticles were spherical with sizes 12-13 nm. The degradation of NB was studied, and an optimal degradation time of 180 min led to 98.6% NB abatement of NB = 0.05 mM, pH = 4, and catalyst loading = 50 mg/100 mL, under visible light. The degradation of NB follows the pseudo-first-order kinetics. The reusability studies indicated the excellent stability of 0.25% Cu-TiO2.

Green Synthesis of CS-TiO2 NPs for Efficient Photocatalytic Degradation of Methylene Blue Dye

The development of a non-malignant and sustainable treatment approach for eradicating mephitic organic dyes from freshwater resources is a daunting task. In a similar vein, the current work investigates the mitigation of methylene blue (MB) dye utilizing titanium dioxide nanoparticles (CS-TiO₂ NPs) synthesized using cannabis sativa (bhang) leaf extract via a greener approach. The CS-TiO₂ NPs are well characterized through XRD, FE-SEM, HR-TEM, UV-Vis spectroscopy, FTIR spectroscopy, and EDS spectroscopy. Microscopic studies confirm that the average particle size distribution of the individual particles was found to be in the range of 12.5 ± 1.5 nm, whereas the average size of the CS-TiO₂ NPs aggregates is 24.5 ± 11.5 nm. Additionally, the synthesized CS-TiO₂ NPs manifested remarkable photocatalytic degradation potential against methylene blue dye with a degradation efficiency of 98.2% and an apparent rate constant of 0.0398 min⁻¹. As a result, this research offers a green/sustainable alternative for water purification.

Fabrication of TiO2/NiO p-n Nanocomposite for Enhancement Dye Photodegradation under Solar Radiation

A p-n nanocomposite based on TiO2 nanotubes (NTs) and NiO nanoparticles (NPs) was designed and optimized in this study to improve the photocatalytic performance of methylene blue (MB). The hydrothermal technique has been used to produce TiO2/NiO nanocomposites with different NiO NPs weight ratios; 1TiO2:1NiO, 1TiO2:2NiO, and 1TiO2:3NiO. The crystal phase, chemical composition, optical properties, and morphology of TiO2/NiO were explored by various techniques. TiO2 NTs have a monoclinic structure, while NiO NPs have a cubic structure, according to the structural study. The bandgap of TiO2 NTs was reduced from 3.54 eV to 2.69 eV after controlling the NiO NPs weight ratio. The TiO2/2NiO nanocomposite showed the best photodegradation efficiency. Within 45 min of solar light irradiation, the efficiency of MB dye degradation using TiO2/2NiO hits 99.5% versus 73% using pure TiO2 NTs. Furthermore, the catalytic photodegradation efficiency did not deteriorate significantly even after five reusability cycles, intimating the high stability of the TiO2/2NiO nanocomposite. This suggests that the loading of NiO NPs into TiO2 NTs lowers the recombination of photo-produced electron/hole pairs and enlarged solar spectral response range, which results in improved photocatalytic activity. The mechanism of charge transfer in the TiO2/NiO and kinetic models were discussed for the photodegradation of MB.

Sn-doped BiOI assisted the excellent photocatalytic performance of multi-shelled ZnO microspheres under simulated sunlight

To deal with the environmental pollution and energy crises, it is indispensable to find green and efficient means to overcome these challenges. Herein, the Sn-doped BiOI modified multi-shelled ZnO heterojunction composite with a high performance are designed and prepared. The results prove the formation of heterojunction structure in the composites and the morphology is shown as the multi-shelled microsphere. The performances of the composites are evaluated by different kinds of antibiotic degradation and H₂-evolution under simulation sunlight irradiation. The measurements present that the Sn-BiOI/ZnO (SBZs) could completely remove ciprofloxacin (CIP) within 100 min, which is 4.18 times that of ZnO in kinetics. Typically, the degradation rate of CIP for SBZ6 is over 99.9%, which is more than 25% higher than that of pure ZnO microspheres. In addition, the rate of H₂ production could reach 3.08 mmol g^-1∙ h^-1, which is 1.79 times of the pure ZnO microspheres. The boosted performance of the composites may originate from the enhanced electronic transmission efficiency and improved separation and recombination efficiency of electrons/holes. The charge transfer mode in the SBZs heterojunction composites is proposed and verified as the Z-scheme by the active species experimental and the possible electron transfer path analysis. Therefore, Sn-doped BiOI is introduced into multi-shelled ZnO microsphere to form contact heterojunction interfacial, which greatly improves the photocatalytic performances of the SBZs. Furthermore, this work supplies a strategy for designing and preparing highly active ZnO-based heterojunction composites, which could effectively address the challenges of environmental remediation and clean energy production.

Highly Efficient Photocatalyst Fabricated from the Chemical Recycling of Iron Waste and Natural Zeolite for Super Dye Degradation

In this paper, Fe2O3 and Fe2O3-zeolite nanopowders are prepared by chemical precipitation utilizing the rusted iron waste and natural zeolite. In addition to the nanomorphologies; the chemical composition, structural parameters, and optical properties are examined using many techniques. The Fe2O3-zeolite photocatalyst showed smaller sizes and higher light absorption in visible light than Fe2O3. Both Fe2O3 and Fe2O3-zeolite are used as photocatalysts for methylene blue (MB) photodegradation under solar light. The effects of the contact time, starting MB concentration, Fe2O3-zeolite dose, and pH value on photocatalytic performance are investigated. The full photocatalytic degradation of MB dye (10 mg/L) is achieved using 75 mg of Fe2O3-zeolite under visible light after 30 s, which, to the best of our knowledge, is the highest performance yet for Fe2O3-based photocatalysts. This photocatalyst has also shown remarkable stability and recyclability. The kinetics and mechanisms of the photocatalytic process are studied. Therefore, the current work can be applied industrially as a cost-effective method for eliminating the harmful MB dye from wastewater and recycling the rusted iron wires.

Engineering the photocatalytic efficiency of nanoscale TiO2 anatase with doped (Nd/Y) and co-doped (Nd–Y/Nd–Sm) lanthanides to decompose the azo dye orange G under UV-VIS irradiation

Nd/Y–TiO2 anatase nanopowders displayed the highest degradation of 96.34% in 105 minutes only.

Construction of SnNb2O6/MgIn2S4 heterojunction photocatalysts with enhanced visible-light-driven activity for tetracycline hydrochloride degradation and Cr(vi) reduction

A novel type II SnNb2O6/MgIn2S4 composite photocatalyst was prepared. The prepared composite photocatalyst exhibited significantly improved photocatalytic activity for Cr(vi) reduction and tetracycline hydrochloride degradation under visible light.

Characterization of Co2+- and Fe3+-Codoped TiO2 Nanomaterials for Photocatalytic Degradation of Organic Pollutants under Visible Light Irradiation

In this study, TiO2 nanomaterials were prepared using a solvothermal method and codoped with Co2+ and Fe3+ ions for the photocatalytic degradation of organic pollutants under visible light. The physicochemical properties of the obtained materials were studied by powder X-ray diffraction, field emission electron scanning microscopy, energy-dispersive X-ray spectroscopy, and nitrogen adsorption isotherms. Optical absorption was characterized by UV-vis absorption spectroscopy. The photocatalytic activities of the prepared materials were evaluated through methylene blue (MB) degradation under visible light irradiation. Results showed the excellent performance of MB degradation investigated on TiO2 samples codoped with Co2+ and Fe3+ in comparison with undoped and Co2+-doped TiO2 samples. The codoped TiO2 samples degraded 85%–90% of MB after 120 min, whereas all the prepared TiO2 samples were composed of pure anatase phase and had a spherical-like shape and mean crystalline size ranging from 6.2 nm to 7.8 determined by Scherrer’s equation. The optical absorption of the TiO2 codoped with Co2+ and Fe3+ was significantly enhanced toward the visible light region. The pseudo-second-order kinetic model fits well for the degradation of MB on as-prepared TiO2 codoped with Co2+ and Fe3+.

Synthesis and Characterization of Sn/Ni Single Doped and Co–Doped Anatase/Rutile Mixed–Crystal Nanomaterials and Their Photocatalytic Performance under UV–Visible Light

Pure and Sn/Ni co–doped TiO2 nanomaterials with anatase/rutile mixed crystal were prepared and characterized. The results show that pure TiO2 is a mixed crystal structure composed of a large amount of anatase and a small amount of rutile. Sn doping promotes the phase transformation from anatase to rutile, while Ni doping inhibits the transformation. Both single doping and co–doping are beneficial to the inhibition of photoinduced charge recombination. Sn doping shows the best inhibitory effect on photogenerated charge recombination, and increases the utilization of visible light, displaying the highest photocatalytic activity. The decolorization degree of methylene blue (MB) by Sn–TiO2 is 79.5% after 150 min. The reaction rate constant of Sn–TiO2 is 0.01022 min−1, which is 5.6 times higher than pure TiO2 (0.00181 min–1).

Photocatalytic degradation of congo red dye using nickel-titanium dioxide nanoflakes synthesized by Mukia madrasapatna leaf extract

Semiconductor photocatalysts are efficient degraders of organic and inorganic waste water pollutants. Herein, we synthesized nickel-titanium dioxide (Ni-TiO₂) nanoflakes using Mukia maderaspatana leafs with the aim of analyzing their photocatalytic degradation potential. Morphological analyses revealed that the nanoflakes were highly agglomerated with an average size of 100 nm. Further, elemental analysis confirmed the presence of Ti, O, and Ni, whereas Fourier transform infrared spectroscopy and X-ray diffraction established the presence of TiO₂ and NiO. We found that photocatalytic degradation of congo red under UV illumination increased with increasing incubation period, demonstrating that Ni-TiO₂ nanoflakes can be used as optimal photocatalysts for the degradation of dyes in waste water.

High Degradation of Methylene Blue Using a New Nanocomposite Based on Zeolitic Imidazolate Framework-8

The development of broad-spectrum ultraviolet- and visible-light photocatalysts constitutes one of the most significant challenges in the field of photocatalytic pollutant removal. Here, the efficiency of the directly prepared nitrogen-doped quantum zeolitic imidazolate framework (ZIF)-8-dot catalyst for the photocatalytic degradation of the methylene blue dye was reported. The prepared catalysts were characterized using Brunauer-Emmett-Teller, X-ray diffraction, ultraviolet-visible spectroscopy, photoluminescence spectroscopy, Fourier transform infrared spectroscopy, transmission electron microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy techniques. Under sunlight irradiation, the 1% nitrogen-doped quantum-ZIF-8-dot catalyst showed 75% photodegradation in half an hour and ≈93% photodegradation after 3 hours compared to ≈87% for the ZIF-8 metal-organic framework. The high performance of the 1% nitrogen-doped quantum-ZIF-8-dot catalyst was attributed to the synergism between the catalyst components, upconverted fluorescence property of nitrogen-doped quantum dots, and charge (electrons-holes) separation. The reactive radical test revealed that the hydroxyl radical was dominant. The step-scheme heterojunction mechanism for photocatalytic degradation was also deduced. The kinetic study through the photocatalytic isotherms revealed that the pseudo-first-order kinetic model can describe the reaction mechanism.

A Review on Metal Ions Modified TiO2 for Photocatalytic Degradation of Organic Pollutants

TiO2 is a semiconductor material with high chemical stability and low toxicity. It is widely used in the fields of catalysis, sensing, hydrogen production, optics and optoelectronics. However, TiO2 photocatalyst is sensitive to ultraviolet (UV) light; this is why its photocatalytic activity and quantum efficiency are reduced. To enhance the photocatalytic efficiency in the visible light range as well as to increase the number of the active sites on the crystal surface or inhibit the recombination rate of photogenerated electron–hole pairs electrons, various metal ions were used to modify TiO2. This review paper comprehensively summarizes the latest progress on the modification of TiO2 photocatalyst by a variety of metal ions. Lastly, the future prospects of the modification of TiO2 as a photocatalyst are proposed.

Photocatalytic study of Ni-N-codoped TiO2 nanoparticles under visible light irradiation

In present paper pure and Ni-N-codoped TiO2 nanoparticles have been synthesized via sol gel technique. Crystal phase formation of as synthesized nanoparticles was determined from x-ray diffraction which confirms the existence of anatase phase of TiO2. The average crystalline size was determined from x-ray diffraction and estimated from Transmission Electron Micrographs found to vary from 24.8 nm to 10.2 nm. The morphology was studied by Field Emission Scanning Electron Microscopy and reveals that the synthesized nanoparticles are highly crystalline, spherical and small agglomerated. It is observed that on doping the agglomeration decreases and is due to relative rates of growth process. The band gap energy was calculated from UV–visible absorption spectroscopy and found to be 3.12, 1.81, 1.69 and 1.53 eV respectively. The appearance of emission bands at 453, 470, 483 and 494 nm in Photoluminescence spectra could be arising from defect energy states caused by oxygen vacancies within the forbidden region of TiO2.The structural formation of the synthesized nanoparticles is investigated from Fourier-transform-infrared and Energy dispersive x-ray spectroscopy measurements. Photocatalytic degradation efficiency of as synthesized nanoparticles against two different dyes (Congo red and Methyl orange) was investigated under visible light source of wavelength 420–520 nm and is found to increase with dopant concentration (x). It is observed that the increase in Photocatalytic degradation efficiency of synthesized nanoparticles is attributed to decrease in carrier recombination rate arises from the decrease in band gap energy. On the basis of these observations it is concluded that the increase in Photocatalytic activity is due to increase in surface area arises from the decrease in average crystalline size of the synthesized nanoparticles.

Strategy for the advanced treatment of simulated tail water of dyeing wastewater based on a short-cut photocatalysis/algal degradation hybrid technology

Refractory organic pollutants in tail water of dyeing wastewater treatment have aroused wide concern. Their efficient and cost-effective removal reduced their threat to public health and ecosystem. Herein, a novel short-cut photocatalysis/algal degradation-based hybrid technology was implemented in efficient removal of methylene blue (MB) in simulated tail water using reliable titanium dioxide and common Chlorella pyrenoidosa, and the mechanisms in processes were emphasized. The treatment efficiency was significantly improved via pretreatment before chemical and biological degradation. MB of 79.71% was concentrated as the adsorption of the modified titanium dioxide and the collection of titanium dioxide by inorganic coagulant. The supernatant with low concentration of MB after coagulation was able to be directly treated by Chlorella pyrenoidosa. MB of 93.7% was degraded and transformed to intermediates in short-cut photocatalysis under visible light in 1 h. The intermediates owning the low biological inhibition were easily further degraded by Chlorella pyrenoidosa in 6 days. Mechanism analysis implied that the modified titanium dioxide was not simple monolayer adsorption, and physical adsorption was dominant. The coagulant played an essential role of charge neutralization in collection of the modified titanium dioxide. The removal of photocatalytic intermediates was divided to fast adsorption of Chlorella pyrenoidosa, low desorption in lag period of algae, and gradual biodegradation that accompanied with the increase of algal cell quantity.

Cost Effective Solvothermal Method to Synthesize Zn-Doped TiO2 Nanomaterials for Photovoltaic and Photocatalytic Degradation Applications

Titanium dioxide (TiO2) is a commonly used wide bandgap semiconductor material for energy and environmental applications. Although it is a promising candidate for photovoltaic and photocatalytic applications, its overall performance is still limited due to low mobility of porous TiO2 and its limited spectral response. This limitation can be overcome by several ways, one of which is doping that could be used to improve the light harvesting properties of TiO2 by tuning its bandgap. TiO2 doped with elements, such as alkali-earth metals, transition metals, rare-earth elements, and nonmetals, were found to improve its performance in the photovoltaic and photocatalytic applications. Among the doped TiO2 nanomaterials, transition metal doped TiO2 nanomaterials perform efficiently by suppressing the relaxation and recombination of charge carriers and improving the absorption of light in the visible region. This work reports the possibility of enhancing the performance of TiO2 towards Dye Sensitised Solar Cells (DSSCs) and photocatalytic degradation of methylene blue (MB) by employing Zn doping on TiO2 nanomaterials. Zn doping was carried out by varying the mole percentage of Zn on TiO2 by a facile solvothermal method and the synthesized nanomaterials were characterised. The XRD (X-Ray Diffraction) studies confirmed the presence of anatase phase of TiO2 in the synthesized nanomaterials, unaffected by Zn doping. The UV-Visible spectrum of Zn-doped TiO2 showed a red shift which could be attributed to the reduced bandgap resulted by Zn doping. Significant enhancement in Power Conversion Efficiency (PCE) was observed with 1.0 mol% Zn-doped TiO2 based DSSC, which was 35% greater than that of the control device. In addition, it showed complete degradation of MB within 3 h of light illumination and rate constant of 1.5466×10−4s−1 resembling zeroth order reaction. These improvements are attributed to the reduced bandgap energy and the reduced charge recombination by Zn doping on TiO2.

Experimentally and theoretically approaches for disperse red 60 dye adsorption on novel quaternary nanocomposites

A comprehensive study that combined both experimental and computational experiments was performed to evaluate the usage of organo-metal oxide nanocomposite for the elimination of disperse red 60 dye (DR) from aqueous solutions. Chitosan was modified by Schiff base to form nanoneedles chitosan-4-chloroacetophenone derivative. The derivatives were then impregnated with CeO₂–CuO–Fe₂O₃ or CeO₂–CuO–Al₂O₃ metal oxides to prepare a novel quarternary organo-metal oxide nanocomposite. The novel nanocomposite, chitosan-4-chloroacetophenone/CeO₂–CuO–Fe₂O₃ (CF) and chitosan-4-chloroacetophenone/CeO₂–CuO–Al₂O₃ (CA) are cheap and effective nano adsorbents that can be used for the uptake of DR from aqueous solution. The CF and CA nano-composites were characterized using different techniques. Moreover, the effect of adsorption parameters (initial DR concentration, time of contact, pH, temperature, and adsorbent mass) as well as CA and CF reusability tests were performed. Langmuir adsorption isotherm and pseudo-second-order kinetics models were best fitted with the adsorption process. The maximum amount of DR adsorbed was 100 mg/g on CF and CA at pH 2 and 4, respectively with a physical spontaneous, and exothermic adsorption process. Monte Carlo (MC) simulation studies indicated the adsorption of DR molecule on the CF and CA surfaces following a parallel mode in most of all studied configurations, confirming the strong interactions between the DR and surfaces atoms of CF and CA. The molecular structure analysis of DR dye adsorbed on the surface of CF and CA indicated that the adsorption process related to Van der Waals dispersion force. Consequently, this helps to trap DR dye molecules on the surface of CF and CA (i.e., physical adsorption), which supports our experimental results.

A carbon membrane-mediated CdSe and TiO2 nanofiber film for enhanced photoelectrochemical degradation of methylene blue

In this study, a carbon membrane-mediated CdSe and TiO₂ ternary film (CdSe/C/TiO₂) was prepared to degrade methylene blue (MB). Carbon membrane and CdSe were introduced to the surface of a TiO₂ nanofiber film via an in situ hydrothermal deposition process successively. The investigation shows that the carbon membrane not only provides a charge transfer channel to promote the transfer of electron from the conduction band of CdSe to that of TiO₂, but also improves the poor conduct between the TiO₂ film and electrolyte. The synergies between the carbon membrane and CdSe can make the ternary system harvest more visible light energy and facilitate the charge transfer property of TiO₂. The current density of CdSe/C/TiO₂ was about 9 folds higher compared with that of pure TiO₂ under UV and visible light irradiations. This ternary hybrid exhibits a superior activity during the photoelectrochemical (PEC) degradation of MB, and 92.43% can be removed after 120 min irradiation, which is improved by 21.14% than that of TiO₂.

A CdSe/C/TiO₂ nanofiber film was prepared for enhanced photoelectrochemical degradation ability, and carbon membrane as a carrier-transfer-channel could promote electron transfer.

Free-standing TiO2 nanotubes decorated with spherical nickel nanoparticles as a cost-efficient electrocatalyst for oxygen evolution reaction

Here, we report significant activity towards the oxygen evolution reaction (OER) of spherical nickel nanoparticles (NPs) electrodeposited onto free-standing TiO2 nanotubes (TNT) via cyclic voltammetry. It has been shown that simple manipulation of processing parameters, including scan rate and number of cycles, allows for formation of the NPs in various diameters and amounts. The polarization data with respect to transmission electron microscopy (TEM) allowed for determination of the diameter and propagation depth of the Ni NPs leading to the highest activity towards the OER with an overpotential of 540 mV at +10 mA cm-2 and Tafel slope of 52 mV per decade. X-ray photoelectron spectroscopy (XPS) indicates the presence of structure defects within Ni NPs whereas Mott-Schottky analysis provides information on the anodically shifted flat band potential and highly increased donor density. The obtained results along with literature studies allowed a proposal of the origin of the enhancement towards the OER. We believe that combination of transition metal-based NPs and TNT provides valuable insight on efficient and low-cost electrocatalysts.

Facile Fabrication of ZnMgAl/LDH/Algae Composites as a Potential Adsorbent for Cr(VI) Ions from Water: Fabrication and Equilibrium Studies

In order to improve the adsorption capacity of natural layered double hydroxyl (LDH) materials, the natural organic sources such as algae containing hydroxyl groups, amino groups, peptide connections, and alginate structures were used to improve LDH for the preparation of ZnMgAl LDH-algae composites (LDH-Ax). The structure of prepared composites was established and characterized via various techniques such as scanning electron microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy. The LDH-A2 sample displayed the highest efficiency for Cr(VI) removal, which reached to 99% at the optimum conditions. The prepared composite LDH-A2 showed high stability and reusability (91.7%) after five cycles. The kinetic studies revealed that the Cr uptake by LDH-A1 is described as pseudo-first order, while the case of LDH-A2 is described as pseudo-second order. This study reported that the easily synthesized LDH-Ax has an interesting environmental approval process to eliminate Cr ions from aqueous media quickly and effectively.

Origin of the enhanced photocatalytic activity of (Ni, Se, and B) mono- and co-doped anatase TiO2 materials under visible light: a hybrid DFT study

The characteristic properties of TiO2 (anatase) make doping necessary to enhance its photocatalytic activity. Herein, a density functional theory (DFT) study using the Heyd-Scuseria-Ernzerhof (HSE) hybrid functional was performed to precisely investigate the effect of mono- and co-doping (Ni, Se and B) on the structural, electronic and optical properties of anatase TiO2. Notably, the origin of the enhanced photocatalytic activity of the modified systems was determined. The response to visible light was enhanced for all the mono- and co-doped materials except for Bint, and the highest absorption coefficient was observed for Se4+ mono-doping and Se/Bint+sub and Ni/Bsub co-doping. The decrease in bandgap is associated with a red shift in the absorption edges with the smallest bandgap calculated for Ni/Bsub (2.49 eV). Additionally, the Ni, Se4+ and Se2- mono-doped systems and Ni/Se4+ co-doped systems are proposed as promising photocatalysts for water splitting applications and further experimental validation. Moreover, the Ni/Bint+sub and Se/Bint+sub co-doped materials can also be valuable photocatalysts for other energy applications due to their enhanced visible light activity and the prolonged lifetime of their produced charge carriers.