Effects of Boron Doping on Photocatalytic Activity and Microstructure of Titanium Dioxide Nanoparticles

Photocatalytic and electrocatalytic degradation of bisphenol A in the presence of graphene/graphene oxide-based nanocatalysts: A review

Bisphenol A (BPA), a widely recognized endocrine disrupting compound, has been discovered in drinking water sources/finished water and domestic wastewater influent/effluent. Numerous studies have shown photocatalytic and electrocatalytic oxidation to be very effective for the removal of BPA, particularly in the addition of graphene/graphene oxide (GO)-based nanocatalysts. Nevertheless, the photocatalytic and electrocatalytic degradation of BPA in aqueous solutions has not been reviewed. Therefore, this review gives a comprehensive understanding of BPA degradation during photo-/electro-catalytic activity in the presence of graphene/GO-based nanocatalysts. Herein, this review evaluated the main photo-/electro-catalytic degradation mechanisms and pathways for BPA removal under various water quality/chemistry conditions (pH, background ions, natural organic matter, promotors, and scavengers), the physicochemical characteristics of various graphene/GO-based nanocatalysts, and various operating conditions (voltage and current). Additionally, the reusability/stability of graphene/GO-based nanocatalysts, hybrid systems combined with ozone/ultrasonic/Fenton oxidation, and prospective research areas are briefly described.

Exploring the effect of boron on the grain morphology change and spectral properties of Eu3+ activated barium tantalate phosphor

The effect of the grain morphology on the photoluminescence, charge transfer band, and decay properties was investigated by xEu3+, yB3+ (x = 10 mol%, y = 0, 5, 15, 30, 50, 70, and 100 mol%) co-doped BaTa2O6 ceramics fabricated by solid-state reaction. X-ray diffractions of the samples showed that the single-phase structure persisted up to 100 mol% and there was an improvement in crystallinity with increasing B3+ concentration. SEM micrographs of the Eu3+, B3+ co-doped grains showed that the flux effect of boron promotes grain growth and elongated grain shape. The PL emissions of the BaTa2O6:xEu3+, yB3+ co-doped phosphors increased up to 100 mol% B3+ concentration, and there was an increase in the intensities of the CTB energy 5D0 → 7F1 transition. The increase in PL may be attributed to the increased grain size leading to a decrease in the surface area (SA)/volume (vol) ratio with increasing B3+ concentration, as well as the improvement in crystallinity. However, the decrease in asymmetry ratio was related to the occupation of centrosymmetric (B) sites and the transformation from a rounded/irregular-like to an elongated/rod-like grain shape which has an increasing effect on the SA/vol ratio. The decreasing trend of the Judd-Ofelt parameters (Ω2, and Ω4) with the increase in boron was related to a high local symmetry of Eu3+ sites, and an increase in the electron density of the surrounding ligands, respectively. The increase in boron led to longer decays in the observed lifetime with bi-exponential characteristics. The CIE diagram and UV lamp photographs of the phosphors showed a color transition from red to orange associated with the increasing magnetic dipole transition. This study may provide an alternative perspective and new strategies to describe the control of grain morphology and luminescence concerning RE-doped phosphors.

Degradation of Organic Dyes by the UCNP/h-BN/TiO2 Ternary Photocatalyst

In this study, upconversion nanoparticles (UCNPs) with a flower-like morphology were prepared using a urea coprecipitation method. A ternary photocatalyst was first prepared using a solvothermal method involving the use of titanium oxide (TiO2), hexagonal boron nitride (h-BN), and UCNPs (Y2O3, Yb3+, and Tm3+) as raw materials. The surface morphology, crystal structure, and functional groups of these materials were then characterized and analyzed through scanning electron microscopy, transmission electron microscopy, X-ray diffraction analysis, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, ultraviolet-visible spectrophotometry, and other techniques. Photocatalytic experiments were also conducted to investigate the effects of different catalyst types, raw material doping ratios, pH values, and catalyst quantities on the photocatalytic degradation of rhodamine B (RhB). The results indicated that doping with h-BN and UCNPs reduced the band gap width of RhB, increased its light absorption rate, and decreased the recombination rate of its photogenerated electrons and holes so that the photocatalytic degradation effect reached 100% within 2 h. After five experimental cycles, the 30% UC-BN-Ti photocatalyst remained highly durable and stable. To investigate the effects of different trapping agents on the degradation of RhB, benzoquinone, isopropanol, and ethylenediaminetetraacetic acid disodium salt were used as free-radical-capturing agents. The results indicated that •O2- was the primary active species in the degradation process. Finally, the pathway and mechanism of the degradation of RhB through ternary composite photocatalysis were identified.

Surface engineering of two-dimensional hexagonal boron-nitride for optoelectronic devices

Two-dimensional hexagonal boron nitride (2D h-BN) is being extensively studied in optoelectronic devices due to its electronic and photonic properties. However, the controlled optimization of h-BN's insulating properties is necessary to fully explore its potential in energy conversion and storage devices. In this work, we engineered the surface of h-BN nanoflakes via one-step in situ chemical functionalization using a liquid-phase exfoliation approach. The functionalized h-BN (F-h-BN) nanoflakes were subsequently dispersed on the surface of TiO2 to tune the TiO2/QDs interface of the optoelectronic device. The photoelectrochemical (PEC) devices based on TiO2/F-h-BN/QDs with optimized addition of carbon nanotubes (CNTs) and scattering layers showed 46% improvement compared to the control device (TiO2/QDs). This significant improvement is attributed to the reduced trap/carrier recombination and enhanced carrier injection rate of the TiO2-CNTs/F-h-BN/QDs photoanode. Furthermore, by employing an optimized TiO2-CNTs/F-h-BN/QDs photoanode, QDs-sensitized solar cells (QDSCs) yield an 18% improvement in photoconversion efficiency. This represents a potential and adaptability of our approach, and pathway to explore surface-engineered 2D materials to optimize the interface of solar energy conversion and other emerging optoelectronic devices.

Photoinduced properties of anodized Ti alloys for biomaterial applications

The photocatalytic properties of anodic oxides on a newly developed TiNbSn and commonly used Ti6Al4V alloys as biomaterials were investigated. The alloys were anodized in an electrolyte of sodium tartrate acid with H2O2 at a high voltage and the mechanism of the photocatalytic and antiviral activities was studied. The anodized TiNbSn and Ti6Al4V exhibited highly crystallized rutile TiO2 and poorly crystallized anatase TiO2, respectively. X-ray photoelectron spectroscopy analysis revealed the presence of oxides of the alloying elements in addition to TiO2. The anodized TiNbSn exhibited higher activities than Ti6Al4V, and electron spin resonance spectra indicated that the number of hydroxyl radicals (⋅OH) generated from the anodized TiNbSn was higher than that from the anodized Ti6Al4V. The results can be explained by two possible mechanisms: the higher crystallinity of TiO2 on TiNbSn than that on the Ti6Al4V reduces the number of charge recombination sites and generates abundant ⋅OH; charge separation in the anodic oxide on TiNbSn due to the electronic band structure between TiO2 and the oxides of alloying elements enhances photo activities. The excellent photoinduced characteristics of the anodized TiNbSn are expected to contribute to the safe and reliable implant treatment.

B-doping mediated formation of oxygen vacancies in Bi2Sn2O7 quantum dots with a unique electronic structure for efficient and stable photoelectrocatalytic sulfamethazine degradation

This study devised a straightforward one-step approach that enabled simultaneous boron (B) doping and oxygen vacancies (OVs) production on Bi₂Sn₂O₇ (BSO) (B-BSO-OV) quantum dots (QDs), optimizing the electrical structure of the photoelectrodes. Under light-emitting diode (LED) illumination and a low potential of 1.15 V, B-BSO-OV demonstrated effective and stable photoelectrocatalytic (PEC) degradation of sulfamethazine (SMT), achieving the first-order kinetic rate constant of 0.158 min^-1. The surface electronic structure, the different factors influencing the PEC degradation of SMT, and the degradation mechanism were studied. Experimental studies have shown that B-BSO-OV exhibits strong visible light trapping ability, high electron transport ability, and superior PEC performance. DFT calculations show that the presence of OVs on BSO successfully reduces the band gap, controls the electrical structure, and accelerates charge transfer. This work sheds light on the synergistic effects of the electronic structure of B-doping and OVs in heterobimetallic oxide BSO under the PEC process and offers a promising approach for the design of photoelectrodes.

Red anatase TiO2 microspheres with exposed major {001} facets and boron-stabilized hydrogen-occupied oxygen vacancies for visible-light-responsive water oxidation

In pursuit of efficient solar energy to chemical energy conversion through band engineering of wide-bandgap photocatalysts such as TiO₂, a compromise occurs between a narrow bandgap and high-redox-capacity photo-induced charge carriers, which impairs the potential advantages associated with the widened absorption range. The key to this compromise is an integrative modifier that can simultaneously modulate both the bandgap and band edge positions. Herein, we theoretically and experimentally demonstrate that oxygen vacancies occupied by boron-stabilized hydrogen pairs (OV_BH) serve as an integrative band modifier. Compared to hydrogen-occupied oxygen vacancies (OV_H), which require the aggregation of nanosized anatase TiO₂ particles, oxygen vacancies coupled with boron (OV_BH) can be easily introduced into large and highly crystalline TiO₂ particles, as shown by density functional theory (DFT) calculations. The coupling with interstitial boron facilitates the introduction of paired hydrogen atoms. The red-colored {001} faceted anatase TiO₂ microspheres with OV_BH benefit from the narrowed bandgap of 1.84 eV and the down-shifted band position. These microspheres not only absorb long-wavelength visible light up to 674 nm but also enhance visible-light-driven photocatalytic oxygen evolution.

Photocatalytic Degradation and Mineralization of Estriol (E3) Hormone Using Boron-Doped TiO2 Catalyst

In this research work, boron-doped titanium oxide (B-TiO2) was prepared by the sol-gel method to investigate its behavior in the degradation of the recalcitrant hormone estriol (E3). The doped photocatalyst was synthesized at different boron/titania ratios of 2, 3, and 5 wt.% of boron with respect to the TiO2 content. The obtained materials were characterized by UV-Vis diffuse reflectance spectroscopy (DRS), X-ray diffraction (XRD), Raman spectroscopy, Scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). The textural properties, specific surface area, and porosity were obtained from N2 adsorption–desorption isotherms by BET and BJH methods, respectively. The photocatalytic performance of each synthesized catalyst was evaluated on the degradation of an aqueous solution (10 mg/L) of estriol (E3) under simulated solar radiation. The variation in the hormone concentration was determined by the HPLC technique, and the mineralization was evaluated by the quantification of total organic carbon (TOC). The obtained results indicated that the catalyst with 3 wt.% of boron incorporation exhibited the best performance on the degradation and mineralization of estriol, achieving its complete degradation at 300 kJ/m2 of accumulated energy and 71% of mineralization at 400 kJ/m2 (2 h) obtaining a non-toxic effluent.

Nanomaterials as Photocatalysts-Synthesis and Their Potential Applications

Increasing demand for energy and environmental degradation are the most serious problems facing the man. An interesting issue that can contribute to solving these problems is the use of photocatalysis. According to literature, solar energy in the presence of a photocatalyst can effectively (i) be converted into electricity/fuel, (ii) break down chemical and microbial pollutants, and (iii) help water purification. Therefore, the search for new, efficient, and stable photocatalysts with high application potential is a point of great interest. The photocatalysts must be characterized by the ability to absorb radiation from a wide spectral range of light, the appropriate position of the semiconductor energy bands in relation to the redox reaction potentials, and the long diffusion path of charge carriers, besides the thermodynamic, electrochemical, and photoelectrochemical stabilities. Meeting these requirements by semiconductors is very difficult. Therefore, efforts are being made to increase the efficiency of photo processes by changing the electron structure, surface morphology, and crystal structure of semiconductors. This paper reviews the recent literature covering the synthesis and application of nanomaterials in photocatalysis.

Surface-Enriched Boron-Doped TiO2 Nanoparticles as Photocatalysts for Propene Oxidation

A series of nanostructured boron-TiO₂ photocatalysts (B-X-TiO₂-T) were prepared by sol-gel synthesis using titanium tetraisopropoxide and boric acid. The effects of the synthesis variables, boric acid amount (X) and crystallization temperature (T), on structural and electronic properties and on the photocatalytic performance for propene oxidation, are studied. This reaction accounts for the remediation of pollution caused by volatile organic compounds, and it is carried out at low concentrations, a case in which efficient removal techniques are difficult and costly to implement. The presence of boric acid during the TiO₂ synthesis hinders the development of rutile without affecting the textural properties. X-ray photoelectron spectroscopy analysis reveals the interstitial incorporation of boron into the surface lattice of the TiO₂ nanostructure, while segregation of B₂O₃ occurs in samples with high boron loading, also confirmed by X-ray diffraction. The best-performing photocatalysts are those with the lowest boron loading. Their high activity, outperforming the equivalent sample without boron, can be attributed to a high anatase and surface hydroxyl group content and efficient photo-charge separation (photoelectrochemical characterization, PEC), which can explain the suppression of visible photoluminescence (PL). Crystallization at 450 °C renders the most active sample, likely due to the development of a pure anatase structure with a large surface boron enrichment. A shift in the wavelength-dependent activity profile (PEC data) and the lowest electron-hole recombination rate (PL data) are also observed for this sample.

B-doped SnO2 nanoparticles: a new insight into the photocatalytic hydrogen generation by water splitting and degradation of dyes

Boron-doped SnO₂ (B:SnO₂) has been synthesized via a facile wet chemical method to deal with increasing energy demand and environment-related issues. Powder XRD confirmed the rutile phase of the synthesized B:SnO₂ nanoparticles. Energy dispersive X-ray analysis and elemental mapping confirmed 1% B doping into SnO₂ lattice. A red shift was observed during the analysis of Raman and FTIR spectral data. The bands in FTIR and Raman spectra confirmed the in-plane and bridging oxygen vacancies in SnO₂ lattice introduced due to B doping. These nanoparticles showed proficiency in photocatalytic hydrogen generation and degradation of crystal violet (CV) and rhodamine B (RhB) dyes. The degradation of CV and RhB dyes in the presence of B:SnO₂ NPs and ethane-1,2-diaminetetracetic acid (EDTA) was found to be 83 and ~ 100%, respectively. To escalate the efficiency of dye degradation, the experiment was performed with different sacrificial agents (EDTA, methanol, and triethanolamine). The maximum hydrogen production rate (63.6184 µmol g^-1 h^-1) was observed for B:SnO₂ along with Pd as co-catalyst, and methanol and EDTA solution as sacrificial agents.

TiO2: A Semiconductor Photocatalyst

Titanium dioxide (TiO2) is considered as an inert and safe material and has been used in many applications for decades. TiO2 have been widely studied, due to its interesting general properties in a wide range of fields including catalysis, antibacterial agents, in civil as nano-paint (self-cleaning) and especially photocatalysis, and that affect the quality of life. Thus, the development of nanotechnologies TiO2 nanoparticles, with numerous novel and useful properties, are increasingly manufactured and used. TiO2 doped with noble metal are good candidates in the performance these applications. The fascinating physical and chemical features of TiO2 depend on the crystal phase, size and shape of particles. For example, varying phases of crystalline TiO2 have different band gaps that rutile TiO2 of 3.0 eV and anatase TiO2 of 3.2 eV, determine the photocatalytic performance of TiO2. This chapter explains basic information on TiO2 and theoretical concepts of nanostructure of TiO2 nanoparticles as a semiconductor photocatalyst.

Developing and Regenerating Cofactors for Sustainable Enzymatic CO2 Conversion

Enzymatic CO2 conversion offers a promising strategy for alleviating global warming and promoting renewable energy exploitation, while the high cost of cofactors is a bottleneck for large-scale applications. To address the challenge, cofactor regeneration is usually coupled with the enzymatic reaction. Meanwhile, artificial cofactors have been developed to further improve conversion efficiency and decrease cost. In this review, the methods, such as enzymatic, chemical, electrochemical, and photochemical catalysis, developed for cofactor regeneration, together with those developed artificial cofactors, were summarized and compared to offer a solution for large-scale enzymatic CO2 conversion in a sustainable way.

Zirconia supported gold-palladium nanocatalyst for NAD(P)H regeneration via two-step mechanism

The regeneration cycle of expensive cofactor, NAD(P)H, is of paramount importance for the bio-catalyzed redox reactions. Here a ZrO₂supported bimetallic nanocatalyst of gold-palladium (Au-Pd/ZrO₂) was prepared to catalyze the regeneration of NAD(P)H without using electron mediators and extra energy input. Over 98% of regeneration efficiency can be achieved catlyzed by Au-Pd/ZrO₂using TEOA as the electron donor. Mechanism study showed that the regeneration of NAD(P)H took place through a two-step process: Au-Pd/ZrO₂nanocatalyst first catalyzed the oxidation of triethanolamine (TEOA) to glycolaldehyde (GA), then the generated GA induced the non-catalytic reducing of NAD(P)⁺to NAD(P)H under an alkaline environment maintained by TEOA. This two-step mechanism enables the decoupling of the regeneration of NAD(P)H in space and time into a catalytic oxidation and non-catalytic reducing cascade process which has been further verified using a variety of electron donors. The application significance of this procedure is further demonstrated both by the favorable stability of Au-Pd/ZrO₂nanocatalyst in 5 successive cycles preserving over 90% of its original activity, and by the excellent performance of the regenerated NADH as the cofactor in the catalytic hydrogenation of acetaldehyde using an ethanol dehydrogenase.

Preferential and efficient degradation of phenolic pollutants with cooperative hydrogen-bond interactions in photocatalytic process

Phenolic pollutants as highly toxic and hazardous organics are widely generated from industrial and domestic process. Phenolic pollutants with different hydroxyl position (catechol, resorcinol, hydroquinone, phenol) were preferentially and efficiently oxidized in photocatalytic process (PC) by designing boron-doped TiO₂ (B-TiO₂).The key role for enhancing the photocatalytic activity of B-TiO₂ was the formation of abundant Ti³⁺ species. The formation of Ti³⁺-O weakened the competitive adsorption of H₂O in aqueous solution and favored the formation of cooperative hydrogen bond on the surface of B-TiO₂, leading to enhanced adsorption of phenolic pollutants. The degradation rate constant of B-TiO₂ (k_B-TiO2) was regardless of the corresponding oxidation potential of phenolic pollutants. The k_B-TiO2 for catechol in photocatalytic process was as high as 3.46 min^-1, which was 18.2, 1.6 times higher than that of biodegradation and ozonation methods, respectively. Of note, the preferential removal mechanism of phenolic pollutants was elucidated by in-situ attenuated total reflectance (ATR)-IR and density functional theory calculation (DFT). The results were helpful for developing new preferential oxidation technologies in HO∙-mediated process for selectively removing low concentration but highly toxic pollutants.

Effect of non-metal doping on the photocatalytic activity of titanium dioxide on the photodegradation of aqueous bisphenol A

Non-metals B, N, P and I were doped into titanium dioxide (TiO₂) to form photocatalyst particles. TiO₂ doped with various ratios of B, N, P and I were thus formed and these photocatalyst particles were bonded to fix each other in a column system under sunlight as a result of the photocatalytic degradation of bisphenol A (BPA). The doped TiO₂ was characterized by X-ray diffraction (XRD), UV-visible absorption spectroscopy, and X-ray photoelectron spectroscopy (XPS) to elucidate the mechanism of doping reaction. Doping with B, N, P and I to form the photocatalyst greatly red-shifted the absorption wavelength, increasing the effectiveness of the photocatalyst in reducing BPA. XPS analysis following doping revealed the bonding of B, N, P, I and other functional groups of the surface of the photocatalyst. Results of an experiment that involved the photocatalysts revealed that BPA degradations of 88%, 94%, 93% and 100% in 66.5 min under sunlight using B, N, P, and I-doped titanium dioxide, respectively. The doped photocatalysts were all superior to the undoped titanium dioxide.

Effect of calcination temperature on the properties and applications of bio extract mediated titania nano particles

In order to deal with the arising environmental issues across the globe at present nano particles with unique properties laid a benchmark in the name of nano catalysis. In this work the significance of calcination temperature on the thermal, electronic, structural and surface properties of a nano catalyst produced by sol-gel method using ultrasonic radiation against the disposal of toxic textile pollutants is studied in detail. The extract of tea leaves has been used as a bio-template during the synthesis to revise the crystallite size, surface area, optical absorption potential, and rate of agglomeration of nano sized grains by regulating their physico-chemical and surface properties. The influence of calcination in the transformation of single phased anatase titania to mixed phase anatase-rutile titania and the corresponding outcome in its photocatalytic activity employed in water treatment applications have been verified. The nano catalyst obtained is characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM), Transition electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), Thermo gravimetric analysis (TGA), Brunaueur Emmett Teller (BET) analysis, UV-Vis diffused reflectance spectroscopy (DRS-UV-Vis) etc. The mesoporosity of the particle was examined using Barrett Joyner Halenda (BJH) model. The enhanced photo catalytic efficiency (about 97.7%) of templated nano titania due to calcination is verified against Congo red, a textile dye under optimized conditions. The nano catalyst produced can be easily separated, recycled to support its economic feasibility.

H2-oxidation driven by its behavior of losing an electron over B-doped TiO2 under UV irradiation

In this work, TiO2 was modified by doping the electron-deficient B element, and then the gas-sensing response of B-TiO2 to H2 under UV irradiation at room temperature in a N2 atmosphere and the oxidation of H2 over B-TiO2 under corresponding conditions were tested. It was found that H2 would accept an electron when adsorbed on the TiO2 surface, while H2 would donate an electron when adsorbed on the B-TiO2 surface. Correspondingly, H2 could not be oxidized over TiO2, but could be oxidized over B-TiO2. This indicated that the oxidation of H2 was dependent on the electron-transfer behavior between H2 and the surface of TiO2 or B-TiO2. Based on the relevant characterization results, it was proposed that H2 could accept an electron from TiO2 due to the higher Fermi level of TiO2, while H2 could donate an electron to B-TiO2 due to the lower Fermi level of B-TiO2 induced by doping B. This indicated that the electron-transfer behavior between H2 and TiO2 could be changed by adjusting the Fermi level of TiO2, while the electron-transfer behavior would further affect the photocatalytic activity of oxidizing H2. This result shows that the doable H2 photocatalytic oxidation in thermodynamics can be controlled by a kinetics factor (H2 losing-an-electron behavior). This work can be applied to provide an understanding of the photocatalytic oxidation behavior of other reactants over semiconductor materials.

Synthesis and Characterization of B/NaF and Silicon Phthalocyanine-Modified TiO2 and an Evaluation of Their Photocatalytic Removal of Carbamazepine

This study investigated the synthesis of two different types of photocatalysts, namely, boron/sodium fluoride co-doped titanium dioxide (B/NaF-TiO2), and its analogue, a dye-sensitized form of silicon-based axial methoxy substituted phthalocyanine (B/NaF-TiO2SiPc). Structural and morphological characterizations were performed via X-ray diffraction (XRD); Fourier transform infra-red (FTIR); N2 adsorption–desorption at 77 K by Brunauer–Emmett–Teller (BET) and Barrett, Joyner, and Halenda (BJH) methods; transmission electron microscopy (TEM); X-ray photoelectron spectroscopy (XPS); and UV–visible absorption spectroscopy. The estimated crystallite size of pure TiO2 and pure B/NaF-TiO2 was 24 nm, and that of B/NaF-TiO2SiPc was 29 nm, whereas particle sizes determined by TEM were 25, 28, and 31 nm for pure TiO2, B/NaF-TiO2 and B/NaF-TiO2SiPc respectively. No significant differences between B/NaF-TiO2 and B/NaF-TiO2SiPc were observed for surface area by (BET) analysis (13 m2/g) or total pore volume by the BJH application model (0.05 cm3/g). Energy band gap values obtained for B/NaF-TiO2 and B/NaF-TiO2SiPc were 3.10 and 2.90 eV respectively, lower than pure TiO2 (3.17 eV). The photocatalytic activity of the synthesized materials was tested using carbamazepine (CBZ) as the model substrate. Carbamazepine removal after 4 h of irradiation was almost 100% for B/NaF-TiO2 and 70% for B/NaF-TiO2SiPc; however, the substrate mineralization proceeded slower, suggesting the presence of organic intermediates after the complete disappearance of the pollutant.

Review of First-Principles Studies of TiO2: Nanocluster, Bulk, and Material Interface

TiO2 has extensive applications in the fields of renewable energy and environmental protections such as being used as photocatalysts or electron transport layers in solar cells. To achieve highly efficient photocatalytic and photovoltaic applications, ongoing efforts are being devoted to developing novel TiO2-based material structures or compositions, in which a first-principles computational approach is playing an increasing role. In this review article, we discuss recent computational and theoretical studies of structural, energetic, electronic, and optical properties of TiO2-based nanocluster, bulk, and material interface for photocatalytic and photovoltaic applications. We conclude the review with a discussion of future research directions in the field.

Photocatalytic partial oxidation of methanol to methyl formate under visible light irradiation on Bi-doped TiO2 via tuning band structure and surface hydroxyls

Preparing visible light responsive catalysts for partial oxidation of methanol to methyl formate is a challenging issue. This work addresses the synthesis, characterization and theoretical calculation of Bi doped TiO₂ catalysts as well as their photocatalytic performance and reaction mechanism for MF synthesis from methanol. The catalysts were prepared by a simple wet chemical method. The results of the characterization and theoretical calculation evidenced that bismuth was intercalated in the lattice of anatase by the substitution of titanium. Impurity levels were formed in the valence band, conduction band and between the two bands. The Bi 6s and 5p orbitals contributed to the formation of the impurity levels. The photo-excited electrons transited from the valence band via impurity levels, formed by Bi 6s orbitals, to the conduction band. The doping of Bi enhanced surface hydroxyls, reduced the band gaps and raised the valence band edges (VBE) of the Bi doped catalyst. The Bi doped catalysts were visible light responsive due to the reduced band gap. The surface hydroxyls were beneficial to the methanol conversion, and the rise of the VBE enhanced the redox potential of the photogenerated holes. Only moderate redox potentials and sufficient surface hydroxyls could lead to high methanol conversion and MF selectivity. This study is of great significance to the development of the photocatalytic synthesis theory and provides a green route for MF synthesis from methanol.

Bi-doped titania is well studied for photocatalytic partial oxidation of methanol to methyl formate under visible light irradiation.

Synergistic Effects of Co-Doping on Photocatalytic Activity of Titanium Dioxide on Glucose Conversion to Value-Added Chemicals

Development of conversion of biomass derivatives in combination with utilization of solar energy by photocatalysts is a promising alternative strategy for biorefineries. The photocatalytic reaction could convert glucose to a mixture of value-added chemicals under UV irradiation. Modifications of titanium dioxide (TiO₂) nanoparticles by metal or metalloid (i.e., B and Ag) and nonmetal (i.e., N) dopants were carried out. The effects of co-doping (i.e., B/N and Ag/N) on physicochemical characteristics of the modified photocatalysts, photocatalytic glucose conversion, and the yields of the target chemical products (i.e., gluconic acid, xylitol, arabinose, and formic acid) were studied. The doping of the photocatalysts by different single dopants could improve the performance in terms of productivity and was further enhanced by the synergism from co-doping. The improvement in catalytic performances of the photocatalysts corresponded with the alterations in physicochemical characteristics of the catalysts resulting from the dopants.

Photodegradation of 4-nitrophenol over B-doped TiO2 nanostructure: effect of dopant concentration, kinetics, and mechanism

The 4-nitrophenol (4-NP) is one of the carcinogenic pollutants listed by US EPA and has been detected in industrial wastewater. This study investigates the photocatalytic degradation of 4-NP with TiO₂ and boron (B)-doped TiO₂ nanostructures. The degradation on undoped and B-doped TiO₂ with various boron loadings (1-7%) was studied to establish a relationship between structure, interface, and photo-catalytic properties. The results of XRD, micro Raman, FTIR, and HRTEM show that the B doping has improved the crystallinity and induces rutile phase along with anatase (major phase). The N₂ adsorption-desorption, SEM-EDX, and XPS indicated that the B induced the formation of mesoporous nanostructures in TiO₂ and occupies interstitial sites by forming Ti-O-B type linkage. The surface area of pure TiO₂ was decreased from 235.4 to 63.3 m²/g in B-TiO₂. The photo-physical properties were characterized by UV-Vis DRS, which showed decrease in the optical band-gap of pure TiO₂ (2.98 eV) to B-TiO₂ (2.95 eV). The degradation results demonstrated that the B doping improved the photocatalytic activity of TiO₂; however, this improvement depends on the B concentration in doped TiO₂. B-doped TiO₂ (> 5% B) showed 90 % degradation of 4-NP, whereas the undoped TiO₂ can degrade only 79 % of 4-NP. The degradation followed pseudo-first-order kinetics with rate constant values of 0.006 min^-1 and 0.0322 min^-1 for pure TiO₂ and B-TiO₂ respectively. The existence of a reduced form of Ti³⁺ on the surface of TiO₂ (as evidence from XPS) was found responsible for enhancement in photocatalytic activity.

A facile analytical method for reliable selectivity examination in cofactor NADH regeneration

This study demonstrates a novel method to quantify selective (1,4-NADH) and unselective products (1,2- and 1,6-NADH) in NADH regeneration using combined UV-Vis spectroscopy and biological assays.

Enhanced visible light photocatalysis by TiO2-BN enabled electrospinning of nanofibers for pharmaceutical degradation and wastewater treatment

Boron nitride (BN) nanosheets are promising support materials for catalysts. A series of TiO₂-BN enabled electrospun nanofibers were synthesized for the photocatalytic treatment of ibuprofen and secondary wastewater effluent under visible light. X-ray photoelectron spectroscopy confirmed the existence of B-O-Ti bonds between the BN nanosheets and TiO₂ nanofibers, resulting in energy rearrangement, narrowed band gaps, and enhanced light utilization efficiency of the TiO₂-BN nanocomposites in the visible light spectrum. Transient photocurrent measurements revealed that the BN enhanced the transport of photogenerated holes from the bulk TiO₂ nanofibers to its surface, resulting in more efficient separation and less recombination of the charge carriers. A kinetic study of ibuprofen degradation indicated the enhanced photocatalytic performance of TiO₂-BN catalysts with a higher BN content in the nanocomposites. The kinetic rate constant of the TiO₂-10% BN catalysts was 10 times higher than that of the pure TiO₂ nanofibers. The degradation of organic contaminants in wastewater followed the same trend as ibuprofen and improved with increasing BN content. The stability of the TiO₂-BN nanocomposites as an effective solar photocatalyst was demonstrated by multiple cycles of wastewater treatment. The results proved that TiO₂-BN is an appealing photocatalyst under visible light.

Multiparameter toxicity screening on a chip: Effects of UV radiation and titanium dioxide nanoparticles on HaCaT cells

Microfluidic screening is gaining attention as an efficient method for evaluating nanomaterial toxicity. Here, we consider a multiparameter treatment where nanomaterials interact with cells in the presence of a secondary exposure (UV radiation). The microfluidic device contains channels that permit immobilization of HaCaT cells (human skin cell line), delivery of titanium dioxide nanoparticles (TNPs), and exposure to a known dose of UV radiation. The effect of single-parameter exposures (UV or TNP) was first studied as a benchmark, and then multiparameter toxicity (UV and TNP) at different concentrations was explored. The results demonstrate a concentration-dependent protective effect of TNP when exposed to UV irradiation.

Bioactive TiNbSn alloy prepared by anodization in sulfuric acid electrolytes

The bioactivity of anodized near-β TiNbSn alloy with low Young's modulus prepared in sulfuric acid electrolytes was examined to explore the osseointegration mechanism with a focus on the role of anodic oxide. Hydroxyapatite (HA) precipitated on the surface of anodic oxide following immersion in Hank's solution, and precipitation accelerated with increase in the sulfuric acid concentration of the electrolyte. HA is formed on the surface of as-anodized oxide without subsequent annealing or hot water (HW) treatment. This outcome differs from that of a previous study using anodized TiNbSn alloy prepared in acetic acid electrolytes requiring for subsequent HW treatment. It was found that the oxide anodized in sulfuric acid electrolyte contains a large amount of internal pores and is highly crystallized thick TiO₂, whereas the same prepared in the acetic acid electrolyte is low crystalline thin TiO₂ containing a small amount of pores. The present anodized TiNbSn alloy is preferred for maintaining the low Young's modulus of the alloy and eliminating the subsequent treatment to increase the Young's modulus. A model to rationalize the bioactivity of the present anodic oxide is proposed based on the series of studies. It is concluded that the sulfuric acid electrolyte is favorable for both HA formation and low Young's modulus, and the bioactivity is attributed to the anodic TiO₂ that facilitates incorporation of bone ingredients.

Effect of trap states on photocatalytic properties of boron-doped anatase TiO2 microspheres studied by time-resolved infrared spectroscopy

The photocatalytic hydrogen and oxygen evolution switching effect in the water splitting of two boron-doped anatase TiO₂ microspheres was elucidated from the viewpoint of trap states.

Photoelectrochemical detection of ultra-trace fluorine ion using TiO2 nanorod arrays as a probe

A photoelectrochemical (PEC) method based on the etching reaction of F ions on the surface of TiO₂ nanorod arrays (TNRs) was proposed for the high sensitivity and selectivity detection of F ions. With the increase of F ion concentration, the surface etching reaction on TNR becomes more intense, resulting in the increased number of surface active sites, the reduction of electron transfer resistance, and the increase of photocurrent density. The prepared TNRs as a PEC probe exhibits a good linear relationship between photocurrent increment and the logarithm of F ion concentration in the range from 0.05 to 1000 nM with an ultra-trace detection limit of 0.03 nM for F ion detection.

A photoelectrochemical (PEC) method based on the etching reaction on TiO₂ nanorod arrays is proposed for detection of F ions.