Fabrication of TiO2 nanofiber assembly from nanosheets (TiO2-NFs-NSs) by electrospinning-hydrothermal method for improved photoreactivity

Remarkable Enhancement of Photocatalytic Activity of High-Energy TiO2 Nanocrystals for NO Oxidation through Surface Defluorination

The superior photocatalytic activity of TiO2 nanocrystals with exposed high-energy (001) facets, achieved through the use of hydrofluoric acid as a shape-directing reagent, is widely reported. However, in this study, we report for the first time the detrimental effect of surface fluorination on the photoreactivity of high-energy faceted TiO2 nanocrystals towards NO oxidation (resulting in a NO removal rate of only 5.9%). This study aims to overcome this limitation by exploring surface defluorination as an effective strategy to enhance the photocatalytic oxidation of NO on TiO2 nanocrystals enclosed with (001) facets. We found that surface defluorination, achieved through either NaOH washing (resulting in an improved NO removal rate of 23.2%) or calcination (yielding an enhanced NO removal rate of 52%), leads to a large increase in the photocatalytic oxidation of NO on TiO2 nanocrystals with enclosed (001) facets. Defluorination processes stimulate charge separation, effectively retarding recombination and significantly promoting the production of reactive oxygen species, including superoxide radicals (·O2-), singlet oxygen (1O2), and hydroxyl radicals (·OH). Both in situ diffuse reflectance infrared Fourier-transform spectroscopy and density functional theory calculations confirm the higher adsorption of NO after defluorination, thus facilitating the oxidation of NO on TiO2 nanocrystals.

Fibrous TiO2 Alternatives for Semiconductor-Based Catalysts for Photocatalytic Water Remediation Involving Organic Contaminants

Water decontamination remains a challenge in several developed and developing countries. Affordable and efficient approaches are needed urgently. In this scenario, heterogeneous photocatalysts appear as one of the most promising alternatives. This justifies the extensive attention that semiconductors, such as TiO₂, have gained over the last decades. Several studies have evaluated their efficiency for environmental applications; however, most of these tests rely on the use of powder materials that have minimal to no applicability for large-scale applications. In this work, we investigated three fibrous TiO₂ photocatalysts, TiO₂ nanofibers (TNF), TiO₂ on glass wool (TGW), and TiO₂ in glass fiber filters (TGF). All materials have macroscopic structures that can be easily separated from solutions or that can work as fixed beds under flow conditions. We evaluated and compared their ability to bleach a surrogate dye molecule, crocin, under batch and flow conditions. Using black light (UVA/visible), our catalysts were able to bleach a minimum of 80% of the dye in batch experiments. Under continuous flow experiments, all catalysts could decrease dye absorption under shorter irradiation times: TGF, TNF, and TGW could, respectively, bleach 15, 18, and 43% of the dye with irradiation times as short as 35 s. Catalyst comparison was based on the selection of physical and chemical criteria relevant for application on water remediation. Their relative performance was ranked and applied in a radar plot. The features evaluated here had two distinct groups, chemical performance, which related to the dye degradation, and mechanical properties, which described their applicability in different systems. This comparative analysis gives insights into the selection of the right flow-compatible photocatalyst for water remediation.

Optical Properties of Electrospun Nanofiber Mats

Electrospun nanofiber mats are usually applied in fields where their high specific surface area and small pore sizes are important, such as biotechnology or filtration. Optically, they are mostly white due to scattering from the irregularly distributed, thin nanofibers. Nevertheless, their optical properties can be modified and become highly important for different applications, e.g., in sensing devices or solar cells, and sometimes for investigating their electronic or mechanical properties. This review gives an overview of typical optical properties of electrospun nanofiber mats, such as absorption and transmission, fluorescence and phosphorescence, scattering, polarized emission, dyeing and bathochromic shift as well as the correlation with dielectric constants and the extinction coefficient, showing which effects may occur and can be measured by which instruments or used for different applications.

Preparation of mesoporous ThO2 nanoparticles: Influence of calcination on morphology and visible-light-driven photocatalytic degradation of indigo carmine and methylene blue

The present article reports the synthesis of thoria nanoparticles (ThO₂ NPs) via sol-gel process and examines the effect of calcination temperature of ThO₂ on the morphology and photocatalytic degradation of indigo carmine (IC) and methylene blue (MB) under visible-light. As-synthesized white crystals of ThO₂ were subjected to calcination at different temperatures, viz. 700 °C (TH-700), 800 °C (TH-800), and 900 °C (TH-900). The effect of calcination temperature on the structural, morphological, thermal, surface area-porosity, and optical properties of ThO₂ NPs were investigated by diverse analytical techniques. XRD patterns show the cubic-space group Fm-3m (225) with parameter a = 5.597 Å and reveals crystallite sizes increased with calcination temperature. The bandgap energy was found to be 1.85 eV, 2.33 eV, and 2.71 eV for TH-700, TH-800, and TH-900 NPs, respectively, calculated by Kubelka-Munk (KM) plot. SEM and TEM unveil that the sample TH-700 calcined at a low temperature of 700 °C yields assembled nanosheets, while at higher temperatures, i.e., 800 °C (TH-800) and 900 °C (TH-900), produces agglomerated nanomaterials. Further, TH-700 sample exhibits enhanced photocatalytic degradation within 120 min for both IC and MB dye than TH-800 and TH-900 counterparts. Among the dyes, IC shows improved photocatalytic efficiency than MB for TH-700, owing to the increased optical absorption and improved separation of photogenerated charge carriers. The reusability study of TH-700 reveals that the catalysts were stable up to four successive cycles with no drastic changes in photocatalytic efficiency. Also, systematic photodisintegration of IC was investigated by Liquid chromatography-mass spectrometry (LC-MS).

Preparation of Au-RGO/TiO2 nanotubes and study on the photocatalytic degradation of ciprofloxacin

Au-RGO/TiO₂ nanotubes were prepared by anodic oxidation and electrochemical deposition, and their performance in the photocatalytic degradation of ciprofloxacin was investigated. The results showed that, compared with TiO₂ nanotubes and RGO/TiO₂ nanotubes, the Au-RGO/TiO₂ nanotubes had the highest ciprofloxacin degradation rate, reaching 96.93% in 180 min of photocatalysis. In addition, the possible degradation products of ciprofloxacin were analyzed by liquid chromatography-mass spectrometry, and the mechanism of degradation of ciprofloxacin by Au-RGO/TiO₂ nanotubes was analyzed.

Facet Dependent Activity of Fe(III) Species Modified TiO2 for Simulated Sunlight Driven Fenton-like Reactions

TiO₂ crystals with different exposed facets are synthesized and modified facilely by depositing Fe(III) species. With more (101) facets exposed, the photoactivity of Fe-TiO₂ is obviously enhanced with peroxymonosulfate (PMS) as oxidant. The degradation rate for 20 ppm Bisphenol A (BPA) on Fe-TiO₂ (101) can achieve 0.219 min^-1, ∼8.5 times faster than that of pure TiO₂ under simulated sunlight irradiation. Photoelectrochemical measurements and density functional theory (DFT) calculations confirm that the interfacial charge transfer (IFCT) on Fe-TiO₂ (101) is stronger than that on Fe-TiO₂ (001) and a faster Fe(III)/Fe(II) transformation rate can be therefore achieved. As a result, the generation of ·OH and ¹O₂ will be accelerated with more (101) facets exposed, thus obtaining better photoactivity. Under the Fe-TiO₂/PMS/Light system, BPA can be effectively degraded in a wide pH range or in the presence of multiple inorganic anions. After five cycles, 100% BPA can still be degraded within 60 min. The study provides new photocatalysts design strategy based on Fe(III)/Fe(II) redox for PMS based photocatalytic oxidation.

Cu2O/SrTi1-xCrxO3 Heterojunction Photocatalyst for the Efficient Degradation of Isopropanol under Visible Light Irradiation

A heterojunction of Cu₂O and Cr-doped SrTiO₃ (SrTi_1-xCr_xO₃) was designed for selective photocatalytic isopropanol (IPA) oxidation under visible light irradiation. The photocatalytic oxidation of IPA was measured in a fixed-bed reactor. Cr dopants can increase the light absorption and improve the activity of the catalyst. The formation of the Cu₂O/SrTi_1-xCr_xO₃ heterojunction can further broaden the absorption range of lights and dramatically increase the photocatalytic activity for selective oxidation of IPA. The 3% Cu₂O/SrTi_0.99Cr_0.01O₃ catalyst can fully convert ∼1000 ppm IPA under illumination in 2 h. The selectivity of acetone is ∼100%. The yield is 83 and 4 times higher than that using SrTiO₃ and SrTi_0.99Cr_0.01O₃ as catalysts, respectively. By measuring the ultraviolet-visible absorption spectra and Mott-Schottky plots, we obtained the band structure of the heterojunction, which shows that the conduction and valence bands of Cu₂O are higher than those of SrTi_1-xCr_xO₃, therefore facilitating the separation and transfer of photogenerated electrons and holes. In addition, electron paramagnetic resonance spectroscopy and radical trapping tests reveal that the generation of hydroxyl and superoxide leads to photocatalytic oxidation of IPA by the heterojunction photocatalyst.

A dual S-scheme TiO2@In2Se3@Ag3PO4 heterojunction for efficient photocatalytic CO2 reduction

The excellent photoresponse of semiconductors enables them to be promising photocatalysts for CO₂ reduction, but practical application is hampered by fast recombination of photogenerated carriers, low CO₂ capture capacity and poor stability. Herein, mesoporous hollow nanospheres of a dual S-scheme titanium dioxide@indium selenide@silver phosphate (TiO₂@In₂Se₃@Ag₃PO₄) heterojunction with a large specific surface area are designed and synthesized. The products of photocatalytic CO₂ reduction are CH₄, CH₃OH and CO with yields of 3.98, 4.32 and 8.2 μmol g^-1 h^-1, respectively, and the photocatalysts exhibit excellent cycle performance. The excellent photocatalytic performance is attributed to the large specific surface area of the samples and the construction of dual S-scheme heterojunctions. The large specific surface area can provide sufficient active sites for photocatalytic activity. Simultaneously, the built-in electric field (IEF) in the dual S-scheme exposed to light can facilitate the migration of photogenerated electrons from the CB of the oxidation photocatalyst (OP) to the VB of the reduction semiconductor (RP), where they recombine with the photogenerated holes on the VB of the RP, leaving behind photogenerated carriers with high redox ability for photocatalytic activity. This work provides new insights into the mechanism and design of highly efficient heterojunction photocatalysts for CO₂ reduction.

Nanoclay- and TiO2 Nanoparticle-Modified Poly(N-vinyl pyrrolidone) Hydrogels: A Multifunctional Material for Application in Photocatalytic Degradation and Adsorption-Based Removal of Organic Contaminants

In recent times, access to clean water has become increasingly difficult and one of the most important problems for the sustainability of life due to environmental pollution. Based on this thought, in this study, a multifunctional hydrogel nanocomposite (nanoclay@TiO₂@PNVP) containing linear poly(N-vinyl pyrrolidone) (PNVP), nanoclay, and TiO₂ nanoparticles was synthesized and used as an adsorbent and photocatalyst for the adsorption-based and photocatalytic degradation-based removal of organic and pharmaceutical pollutants such as methylene blue (MB) and sildenafil citrate (SLD). The modification of the hydrogel with TiO₂ nanoparticles and nanoclay aimed to increase the adsorption capacity of the PNVP hydrogel as well as to gain photocatalytic properties for the effective removal of organic contaminants. This hybrid material, which can be cleaned in two different ways, can be reused and recycled at least 10 times. Characterization studies were carried out using Fourier transform infrared spectroscopy, scanning electron microscopy, Raman spectroscopy, thermogravimetric analysis, differential thermogravimetry, and viscosimetry techniques. Optimization studies for the adsorption-based removal of organic contaminants were carried out on MB and SLD as model organic compounds. The optimum parameters for MB were found at pH 10 of the sample solution when 50 mg of the nanoclay@TiO₂@PNVP hydrogel nanocomposite was used for 420 min of contact time. It was observed that 99% of the MB was photocatalytically degraded within 150 min at pH 10. Our material had multifunctional applicability properties, showing high adsorption and photocatalytic performances over 99% for at least 10 times of use. For the removal of organic and pharmaceutical contaminants from wastewater, the synthesized material can be used in two treatment processes separately or in combination in one step, providing an important advantage for its usability in environmental applications.

Nanomaterials photocatalytic activities for waste water treatment: a review

Water is necessary for the survival of life on Earth. A wide range of pollutants has contaminated water resources in the last few decades. The presence of contaminants incredibly different dyes in waste, potable, and surface water is hazardous to environmental and human health. Different types of dyes are the principal contaminants in water that need sudden attention because of their widespread domestic and industrial use. The toxic effects of these dyes and their ability to resist traditional water treatment procedures have inspired the researcher to develop an eco-friendly method that could effectively and efficiently degrade these toxic contaminants. Here, in this review, we explored the effective and economical methods of metal-based nanomaterials photocatalytic degradation for successfully removing dyes from wastewater. This study provides a tool for protecting the environment and human health. In addition, the insights into the transformation of solar energy for photocatalytic reduction of toxic metal ions and photocatalytic degradation of dyes contaminated wastewater will open a gate for water treatment research. The mechanism of photocatalytic degradation and the parameters that affect the photocatalytic activities of various photocatalysts have also been reported.

Facile Fabrication of Durable Biochar/H2-TiO2 for Highly Efficient Solar-Driven Degradation of Enrofloxacin: Properties, Degradation Pathways, and Mechanism

Widespread application of TiO₂ for degradation of antibiotics is restricted by mainly the low photodegradation efficiency under solar irradiation. To expand the application of TiO₂, the key factors that should be improved are visible-light response, yield of electrons and holes, and durability. Herein, we report a visible-light responsive and durable sugarcane-bagasse-derived biochar supported hydrogenated TiO₂ (HSCB/H₂-TiO₂) photocatalyst with higher electron production fabricated by a facile one-pot hydrogenation. Mild hydrogenation temperature preserved the lotus-stem-like structure of sugarcane bagasse and gave the photocatalyst great separability. The superior durability of HSCB/H₂-TiO₂ was demonstrated by 12 rounds of repeated degradation of methylene blue (MB). In addition, the electron paramagnetic resonance (EPR) results demonstrated that the biochar skeleton contains abundant persistent free radicals (PFRs), which can provide excess electrons to form more ^•O₂ ^-. Meanwhile, radical quenching experiment and EPR radical trapping results also revealed that ^•O₂ ^- was the most dominant species for enrofloxacin (ENR) degradation. Thus, the as-fabricated photocatalyst shows excellent solar-driven degradation of ENR, and 95.6% of ENR was degraded in 180 min under simulated solar irradiation. Possible ENR degradation pathways and mechanism are also proposed based on the identified intermediates.

Improving light absorption and photoelectrochemical performance of thin-film photoelectrode with a reflective substrate

The charge separation/transport efficiency is relatively high in thin-film hematite photoanodes in which the distance for charge transport is short, but simultaneously the high loss of light absorption due to transmission is confronted. To increase light absorption in thin-film Fe₂O₃:Ti, commercial substrates such as Cu foil, Ag foil, and a mirror are adopted acting as back-reflectors and individually integrated with the Fe₂O₃:Ti electrode. The promotion effect of the commercial back-reflectors on the light absorption efficiency and photoelectrochemical (PEC) performance of the hydrothermally prepared Fe₂O₃:Ti electrodes with a variety of film thicknesses is investigated. As a result, Ag foil and the mirror show favorable and equal efficacy while the promoting effect of Cu foil is limited. In addition, the photocurrent increment achieved by the Ag back-reflector decreases linearly along with the logarithmic of the film thickness and the optimized film thickness of the Fe₂O₃:Ti electrode is decreased from 520 to 290 nm. The high durability of Ag foil in the alkaline electrolyte during solar light irradiation is demonstrated. Furthermore, the reflective substrate also shows a promotion effect on the BiVO₄ photoanode and CuBi₂O₄ photocathode, as well as the unbiased photocurrent from a tandem cell constituted by TiO₂ and CuBi₂O₄.

The charge separation/transport efficiency is relatively high in thin-film hematite photoanodes in which the distance for charge transport is short, but simultaneously the high loss of light absorption due to transmission is confronted.

One-step calcination synthesis of WC–Mo2C heterojunction nanoparticles as novel H2-production cocatalysts for enhanced photocatalytic activity of TiO2

A WC–Mo2C@C modified-TiO2 (WC–Mo2C@C/TiO2) photocatalyst was prepared by loading WC–Mo2C@C heterojunction nanoparticles on TiO2 surface and its H2-production rate was 90.3, 3.6, and 2.5 times higher than that of TiO2, Mo2C@C/TiO2, and WC@C/TiO2, respectively.

Fe1 /TiO2 Hollow Microspheres: Fe and Ti Dual Active Sites Boosting the Photocatalytic Oxidation of NO

Recently, single-atom catalysts have aroused extensive attention in fields of clean energy and environmental protection due to their unique activity and efficient utilization of the active atoms. It is of great importance but still remains a great challenge to unveil the effect of single atoms on precise catalysis. Herein, it is reported that doping TiO₂ hollow microspheres (TiO₂ -HMSs) with single atomic Fe can boost the photoreactivity of TiO₂ -HMSs towards NO oxidation due to the synergistic effects of atomically dispersed Fe and bonded Ti atom which act as dual active sites. The atomically dispersed Fe atoms occupy the subsurface Ti vacancies, and the interaction between Ti 3d and Fe 3d orbitals result in the formation of FeTi bond. Single atomic Fe modulates the electronic structure of the bonded Ti atoms by electron transfer, which facilitates the adsorption and activation of NO and O₂ at Fe and bonded Ti sites, respectively. In addition, the introduction of single atomic Fe sharply suppresses the production of toxic NO₂ byproduct. The synergistic effects of the dual active sites then cause a drastic promotion in photocatalytic oxidation of NO.

Crystalline Carbon Nitride Supported Copper Single Atoms for Photocatalytic CO2 Reduction with Nearly 100% CO Selectivity

Single metal atom photocatalysts have received widespread attention due to the rational use of metal resources and maximum atom utilization efficiency. In particular, N-rich amorphous g-C₃N₄ is always used as a support to anchor single metal atoms. However, the enhancement of photocatalytic activity of g-C₃N₄ by introducing a single atom is limited due to the bulk morphology and the excess defects of amorphous g-C₃N₄. Here, we report crystalline g-C₃N₄ nanorod supported copper single atoms by molten salts and the reflux method. The prepared single Cu atoms/crystalline g-C₃N₄ photocatalyst (Cu-CCN) shows highly selective and efficient photocatalytic reduction of CO₂ under the absence of any cocatalyst or sacrificial agent. The introduction of single Cu atoms can be used as the CO₂ adsorption site, thus increasing the adsorption capacity of Cu-CCN samples to CO₂. Theoretical calculation results show that reducing CO₂ to CH₄ on Cu-CCN samples is an entropy-increasing process, whereas reducing CO₂ to CO is an entropy-decreasing process. As a result, the Cu-CCN samples exhibited enhanced photocatalytic CO₂ reduction with nearly 100% selective photocatalytic CO₂ to CO conversion. The mechanism of photocatalytic CO₂ reduction over Cu-CCN samples was proposed based on in situ Fourier transform infrared spectra, X-ray absorption spectroscopy, and density functional theory calculation. This work provides an in-depth understanding of the design of photocatalysts for enhancing active sites of the reactants.