Synthesis of N-Doped TiO2 for Efficient Photocatalytic Degradation of Atmospheric NOx

Advances in Carbon-Based Aerogels for CO2 Capture: Fundamental Design Strategies and Technological Progress

Carbon-based aerogels have garnered significant attention for CO2 capture owing to their low-cost precursors, tunable structures, and high porosity. Their performance in CO2 adsorption is intricately linked to their microstructural and textural features, including pore size distribution, surface area, and surface chemistry. Micropores (<2 nm) are particularly effective due to their size compatibility with CO2 molecules, while surface functional groups enhance adsorption through hydrogen bonding and electrostatic interactions. Strategic design approaches have focused on tailoring these properties to optimize CO2 uptake under realistic conditions. This review provides a comprehensive overview of recent advancements in the structural engineering of carbon aerogels, emphasizing the role of hierarchical porosity and heteroatom doping (nitrogen, oxygen, sulfur, etc.) in enhancing adsorption capacity and selectivity. Experimental and theoretical studies have highlighted how the synergistic control of microstructure and surface chemistry leads to superior adsorption performance. Furthermore, this review identifies current challenges, such as limited structural stability and insufficient mechanistic understanding, which hinder further progress. Future research directions are proposed, including advanced pore architecture control, functional group engineering, and the integration of in situ characterization techniques. Overall, this review serves as a guide for the rational design of next-generation carbon-based aerogels tailored for efficient and scalable CO2 capture technologies.

Photocatalytic performance of N-doped Ti3O5 nano-catalyst for phenolic compounds removal from industrial wastewaters

This study is focused on the synthesis and evaluation of TiO2 and N-doped Ti3O5 for the photocatalytic degradation of phenol as a noxious substance commonly present in the industrial process effluents with harmful effects on human and the environment. The research addresses the critical environmental challenge posed by phenol-contaminated effluents from petrochemical industries. Leveraging Response Surface Methodology with Box-Behnken design, 17 experiments were conducted to analyze the impact of independent variables such as photo-catalyst dosage, pH, and irradiation time on degradation efficiency. Notably, the average crystallite sizes were determined as 20 nm for TiO2 and 58.3 nm for N-doped Ti3O5. Energy bandgap assessments show enhanced performance in N-Ti3O5 compared to TiO2 under sunlight. Energy bandgaps of N-Ti3O5 and TiO2 were obtained as 2.45 and 2.75 eV, respectively. The study emphasizes the impact of initial pH on the photocatalytic degradation process, highlighting the superior performance of N-Ti3O5 under neutral conditions. The interfacial charge alteration of N-Ti3O5 based on pH plays a pivotal role in dispersion and adsorption dynamics, influencing the photocatalytic removal efficiency significantly. In this study, a significant improvement in photocatalytic degradation of an industrial wastewater containing phenolic compounds, with maximum efficiencies of 99.87%, 99.78% and 99.779 under UV, visible and sunlight was observed, respectively. The optimal conditions for phenol degradation were pH = 7, 1 g/L of catalyst, and irradiation time = 30 min under low intensity UV (18 W), visible light (18 W) and sunlight, resulting in 99.823% phenol degradation. The synthesized N-doped Ti3O5 showed excellent stability and recyclability for the treatment of phenolic wastewaters. This research not only advances the understanding of Ti3O5-based photo-catalysts but also provides a practical, efficient solution for treating phenol-contaminated industrial wastewaters. The findings of this study have significant implications for environmental remediation in the petrochemical sector.

Effect of doping in TiO2/chitosan composite on adsorptive-photocatalytic removal of gallic acid from water

Gallic acid (GA) has emerged as a low biodegradable and high acidity industrial effluent. Due to mutagenic and carcinogenic nature of GA, it becomes essential to remove it from wastewater. Different chemical, physical and biological methods are being used for this purpose. Photocatalytic degradation is found to be promising method. In the present study N-doped titanium oxide and chitosan composites are used for the photodegradation of gallic acid. An attempt has been made to combine C from chitosan with undoped and N-doped TiO2 so as to produce composites that can suppress the electron-hole recombination, and reduce band gap thus enhancing their catalytic and adsorptive properties. The morphology and surface properties of the synthesized material were determined using techniques such as FTIR, XRD, XPS, BET, PL and SEM-EDX. The formation of spherical TiO2 and N-doped TiO2 occurred in anatase phase, over chitosan. The TiO2/chitosan (TC) and N- TiO2/chitosan (NTC) composites exhibited outstanding photodegradation activity 81% and 92.2% for the GA under visible irradiation (λ > 400 nm) at acidic pH. The desired outcomes of the nitrogen and carbon doping in the metal oxide (NTC) include a highly homogenous surface, a lowered band gap, an increase in the material's surface area, improved reusability, and a decrease in photoluminescence, which suggests that the material's electron-hole recombination is delayed. The purpose of the current study is to gain an understanding of how doping (C/N) affects the development of a photocatalyst that may be used to remove GA from industrial effluent.

Fabrication of Reduced Graphene Oxide Decorated with Nonmetal-Doped Nanotitania: An Efficient Visible Light-Driven Photocatalyst and Sterilizing Agent for Microbial Cells

The present study pertains to the fabrication of a visible light-responsive nanocomposite of nitrogen and sulfur-doped TiO2 anchoring reduced graphene oxide (NSNTG) using a facile microwave method for enhanced photocatalytic activity. Two other nanocomposites, TiO2/rGO (NTG) and nitrogen-doped TiO2/rGO (NNTG), were also synthesized by using the same method. X-ray diffraction (XRD) and Raman spectroscopy were employed to confirm the presence of the crystalline anatase TiO2 phase. Elemental composition and formation of a homogeneous dispersion of modified TiO2 on the GO surface were explored using Field-emission scanning electron microscopy (FESEM) with energy-dispersive X-ray (EDX), and transmission electron microscopy (TEM). X-ray photoelectron spectroscopy (XPS) and photoluminescence (PL) studies revealed surface composition, chemical state, and the presence of oxygen vacancy defects. A lower bandgap energy and stronger absorption in the visible region were confirmed by UV-visible diffuse reflectance spectroscopy (DRS) analysis. Mott-Schottky analysis revealed the flat band potentials and band alignment of NTG, NNTG, and NSNTG, indicating n-type semiconductor behaviors with flat band potential values of -0.50, -0.60, and -0.68 V, respectively, providing insights into their charge transfer processes. The high photocurrent response in NSNTG facilitates efficient charge migration by inhibiting charge recombination, aligning with the results from PL and EIS measurements. In addition, the large surface area (233.0 m2/g) and a small pore size distribution (7.8 nm) of NSNTG nanocomposites were confirmed using N2 adsorption-desorption analysis, supporting enhanced adsorption of organic pollutants. The photocatalytic activity of the synthesized nanocomposites was studied by the degradation of organic dyes under visible light; NSNTG exhibited higher removal rates, 97 and 90% within 35 and 60 min, for methylene blue (MB) and rhodamine B (RhB), respectively. The optimal conditions for degradation were pH 8, dye concentration of 50 mg/L, and photocatalyst dosage of 50 mg. Mineralization rates evaluated from TOC analysis were 85.21 and 82.30% for MB and RhB, respectively. The key reactive species involved in photocatalytic degradation were identified as photogenerated hydroxyl radicals, holes, and superoxide radicals. The synthesized nanocomposites were also tested for their antimicrobial efficacy against Gram-negative and Gram-positive bacteria, by the disc diffusion method, NSNTG exhibited a maximum zone of inhibition against Bacillus subtilis and Staphylococcus aureus, comparable to gentamycin. This study outlines the potential of NSNTG as a cost-effective, high-yield, and reusable material for environmental applications.

Characterization of novel solar based nitrogen doped titanium dioxide photocatalytic membrane for wastewater treatment

The increasing presence of microbial and emerging organic contaminants pose detrimental effects on the environment and ecosystem such as diseases, pandemics and toxicity. Most of these synthetic pollutants are biorecalcitrant and therefore persist in the environment. Conventional water treatment methods are not effective thereby necessitating the development of advanced techniques such as photocatalysis and membrane processes. In this study, visible light-driven photocatalytic membrane was synthesized through the immobilization of nitrogen-doped nanoparticles onto the polyvinylidene fluoride (PVDF) membrane and performance evaluated with E.coli microbial contaminant removal. Characterization was done using Fourier transform infrared spectra, X-ray diffraction (XRD), water contact angle, Scanning Electron Microscopy-Energy Dispersive X-ray (SEM-EDX). The Nitrogen-doping of titanium dioxide red-shifted the light absorption to a visible range of 440 nm from 400 nm. Nitrogen dopant was detected at 1420 cm-1and 1170 cm-1 for nitrogen doped nanoparticles and 1346-1417 cm-1 for nitrogen doped titanium dioxide PVDF membrane. SEM-EDX confirmed presences of nitrogen in nitrogen doped titanium dioxide nanoparticles on membrane surface with nitrogen elemental composition of 0.01 % wt. The water contact angle reduced by 81.39o from 120.14o to 38.75o because of PVA immobilization of nitrogen-doped titanium dioxide and glutaraldehyde crosslinking. Nitrogen doping resulted in visible light active photocatalytic membranes with better hydrophilicity and fouling resistance. 8.42 E.coli log removal and a relative flux of 0.35 was obtained within 75 min. The developed photocatalytic membrane enables the use of sunlight hence a less costly method for decontamination of wastewater.

A mesoporous Mo and N Co-doped TiO2 nanocomposite with enhanced photocatalytic efficiency

This study reports the synthesis of a mesoporous Mo and N codoped anatase TiO2 nanocomposite with many oxygen vacancies using a simple one-step hydrothermal method and subsequent calcination treatment. Both Mo and N were effectively co-incorporated into the anatase phase of TiO2 without MoOx phase segregation. The codoped catalyst demonstrated a mesoporous architecture with a surface area of 107.48 m2 g-1 and a pore volume of 0.2974 cm3 g-1. X-ray photoelectron spectroscopy confirmed that both Mo and N dissolved in the TiO2 lattice and created induced oxygen vacancies. The interaction of the dopants (Mo and N) and oxygen vacancies clearly affected TiO2 crystal formation. Photocatalytic performance of the nanocomposite was investigated in terms of the decomposition of methyl orange at a concentration of 50 mg L-1 in an aqueous solution. The results revealed a significant methyl orange degradation of up to 99.6% after 30 min irradiation under a UV light. The impressive performance of the nanocomposite is assigned to the synergetic effect of important factors, including the co-doping of metallic (Mo) and non-metallic (N) elements, oxygen vacancy defects, bandgap, crystallite size, mesoporous structure, and BET surface area.

Remarkable photocatalytic performances towards pollutant degradation under sunlight and enhanced electrochemical properties of TiO2/polymer nanohybrids

In this work, TiO₂-based nanocomposites containing polyaniline (PANI), poly(1-naphthylamine) (PNA), and polyindole (PIN) were synthesized by effective and simple routes and posteriorly employed as photocatalysts and supercapacitors. Characterization techniques such as XRD, FTIR, FESEM, UV, and PL were employed to investigate the structural, morphological, and optical properties of materials. XRD analysis confirmed the successful formation of TiO₂ and TiO₂/polymer nanocomposites. PANI, PNA, and PIN polymers were well distributed on the surface of TiO₂ nanoparticles and were investigated/explored from the FESEM analysis. The visible light absorption and the recombination rate of photogenerated charge carriers were confirmed by the UV-Vis and PL analysis. The photocatalytic properties of the nanocomposites were investigated towards malachite green (MG) dye degradation under sunlight. The dye degradation efficiency followed the order TiO₂/PNA > TiO₂/PANI > TiO₂ > TiO₂/PIN. The higher efficiency of TiO₂/PNA can be associated with its smaller bandgap energy compared to the other materials. Electrochemical properties of materials were also examined by cyclic voltammetry and galvanostatic charge-discharge measurements using a three-electrode experiment setup in an aqueous electrolyte. TiO₂/PNA nanocomposite showed higher supercapacitor behavior compared to the other materials due to higher electrical conductivity of PNA and redox potential of TiO₂ (pseudocapacitance).

Real-Time Degradation of Indoor Formaldehyde Released from Actual Particle Board by Heterostructured g-C3N4/TiO2 Photocatalysts under Visible Light

Indoor formaldehyde pollution causes a serious threat to human health since it is uninterruptedly released from wooden furniture. Herein, we prepared a g-C3N4-modified TiO2 composite photocatalyst and coated it on the surface of a commercial artificial particle board with the assistance of melamine formaldehyde adhesive. The g-C3N4/ TiO2 coating was then used to degrade formaldehyde which was released in real-time from the particle board under the irradiation of visible light. The results showed that compared with pure TiO2, the g-C3N4/ TiO2 composite with a heterojunction structure had a lower band gap energy (~2.6 eV), which could effectively capture luminous energy from the visible light region. Under continuous irradiation, the g-C3N4/ TiO2 photocatalytic coating was capable of degrading more than 50% of formaldehyde constantly released from the particle board. In the meantime, the photocatalytic coating also exhibited promising catalytic stability towards various formaldehyde release speeds, air flow velocities and environmental humidities. The hydroxyl radical and superoxide radical were found to be the predominant active species which triggered formaldehyde degradation. This study provides a feasible and practical approach for the improvement in indoor air quality through photocatalyst surface engineering.

The Use of Electrochemical Methods to Determine the Effect of Nitrides of Alloying Elements on the Electrochemical Properties of Titanium β-Alloys

Titanium beta alloys represent the new generation of materials for the manufacturing of joint implants. Their Young's modulus is lower and thus closer to the bone tissue compared to commonly used alloys. The surface tribological properties of these materials should be improved by ion implantation. The influence of this surface treatment on corrosion behaviour is unknown. The surface of Ti-36Nb-6Ta, Ti-36Nb-4Zr, and Ti-39Nb titanium β-alloys was modified using nitrogen ion implantation. X-ray photoelectron spectroscopy was used for surface analysis, which showed the presence of titanium, niobium, and tantalum nitrides in the treated samples and the elimination of less stable oxides. Electrochemical methods, electrochemical impedance spectra, polarisation resistance, and Mott-Schottky plot were measured in a physiological saline solution. The results of the measurements showed that ion implantation does not have a significant negative effect on the corrosion behaviour of the material. The best results of the alloys investigated were achieved by the Ti-36Nb-6Ta alloy. The combination of niobium and tantalum nitrides had a positive effect on the corrosion resistance of this alloy. After surface treatment, the polarization resistance of this alloy increased, 2.3 × 10⁶ Ω·cm², demonstrating higher corrosion resistance of the alloy. These results were also supported by the results of electrochemical impedance spectroscopy.

Effect of Thermal Treatment of Symmetric TiO2 Nanotube Arrays in Argon on Photocatalytic CO2 Conversion

Symmetric titania nanotube arrays (TiO2 NTs) are a well-known photocatalyst with a large surface area and band edge potentials suitable for redox reactions. Thermal treatment of symmetrical arrays of TiO2 nanotubes in argon was used to change the carbon content of the samples. The influence of the carbon content in the structure of symmetrical TiO2 NTs on their photoelectrochemical properties and photocatalytic activity in the conversion of CO2 into organic fuel precursors has been studied. The structure, chemical, and phase composition of obtained samples were studied by X-ray analysis, Raman spectroscopy, and SEM with energy dispersive analysis. It is established that carbon-related defects in the samples accumulate electrons on the surface required for the CO2 conversion reaction. It has been shown for the first time that varying the carbon content in symmetric TiO2 NTs arrays by annealing at different temperatures in argon makes it possible to control the yield of methane and methanol in CO2 conversion. It is revealed that too high a concentration of carbon dangling bonds promotes the growth of CO2 conversion efficiency but causes instability in this process. The obtained results show a high promise of symmetric carbon-doped TiO2 NTs arrays for the photocatalytic conversion of CO2.

Visible-Light-Active N-Doped TiO2 Photocatalysts: Synthesis from TiOSO4, Characterization, and Enhancement of Stability Via Surface Modification

This paper describes the chemical engineering aspects for the preparation of highly active and stable nanocomposite photocatalysts based on N-doped TiO₂. The synthesis is performed using titanium oxysulfate as a low-cost inorganic precursor and ammonia as a precipitating agent, as well as a source of nitrogen. Mixing the reagents under a control of pH leads to an amorphous titanium oxide hydrate, which can be further successfully converted to nanocrystalline anatase TiO₂ through calcination in air at an increased temperature. The as-prepared N-doped TiO₂ provides the complete oxidation of volatile organic compounds both under UV and visible light, and the action spectrum of N-doped TiO₂ correlates to its absorption spectrum. The key role of paramagnetic nitrogen species in the absorption of visible light and in the visible-light-activity of N-doped TiO₂ is shown using the EPR technique. Surface modification of N-doped TiO₂ with copper species prevents its intense deactivation under highly powerful radiation and results in a nanocomposite photocatalyst with enhanced activity and stability. The photocatalysts prepared under different conditions are discussed regarding the effects of their characteristics on photocatalytic activity under UV and visible light.

S- and N-Co-Doped TiO2-Coated Al2O3 Hollow Fiber Membrane for Photocatalytic Degradation of Gaseous Ammonia

This study successfully prepared and tested sulfur- and nitrogen-co-doped TiO₂-coated α-Al₂O₃ (S,N-doped TiO₂/Al₂O₃) hollow fiber (HF) membranes for efficient photocatalytic degradation of gaseous ammonia (NH₃). Thiourea was used as a sulfur- and nitrogen-doping source to produce a S,N-doped TiO₂ photocatalyst powder. For comparative purposes, undoped TiO₂ powder was also synthesized. Through the application of a phase-inversion technique combined with high-temperature sintering, hollow fibers composed of α-Al₂O₃ were developed. Undoped TiO₂ and S,N-doped TiO₂ photocatalyst powders were coated on the α-Al₂O₃ HF surface to obtain undoped TiO₂/Al₂O₃ and S,N-doped TiO₂/Al₂O₃ HF membranes, respectively. All prepared samples were characterized using XRD, TEM, XPS, UV-Vis, SEM, BET, FT-IR, and EDS. S and N dopants were confirmed using XPS and UV-Vis spectra. The crystal phase of the undoped TiO₂ and S,N-doped TiO₂ photocatalysts was a pure anatase phase. A portable air purifier photocatalytic filter device was developed and tested for the first time to decrease the amount of indoor NH₃ pollution under the limits of the lachrymatory threshold. The device, which was made up of 36 S,N-doped TiO₂/Al₂O₃ HF membranes, took only 15-20 min to reduce the level of NH₃ in a test chamber from 50 ppm to around 5 ppm, confirming the remarkable performance regarding the photocatalytic degradation of gaseous NH₃.

A Study on the Evaluation Methods of Nitrogen Oxide Removal Performance of Photocatalytic Concrete for Outdoor Applications

In Korea, the issue of particulate matter pollution is growing, and many solutions are being developed to deal with it. Photocatalytic technology has been found to be helpful in removing precursors such as nitrogen oxides that cause particulate matter. In a microcosm setup, ISO 22197-1 has been successfully used to quantify the removal of nitrogen oxides from the specimen to which the photocatalyst is applied. However, owing to a lack of suitable tools, on-site measurement of real-scale efficacy is difficult. Depending on the substrate and surrounding circumstances at the application location, the photocatalyst may function at varying levels. Additionally, the expected photocatalytic effect may differ depending on the ambient air quality and sunlight irradiation intensity. This article describes two approaches for studying outdoor concrete photocatalysis. Standard gas measurement and dual-reactor measurement are the recommended evaluation approaches. The standard gas measurement method was found useful for assessing the applied photocatalyst itself as an outcome of field assessment. The performance of photocatalysts at different sites was found to be mutually exclusive and comparable. Over 180 min, on a building roof deck, the NO removal by the standard gas method was 0.68 ppm, whereas, at two shaded locations, the removal amount was 0.51 ppm (side wall) and 0.24 ppm (underpass) for 300 min. The dual reactor measurement approach, on the other hand, was discovered to be one of the most suitable methods for assessing how much of an improvement there has been in the air quality in areas where photocatalysts have been placed.

Investigation of photocatalytic performance of titania based hybrid nanocomposite structure for dilapidation of organic contaminants

This research paper attempt to provide the photocatalytic performance of nitrogen ion (N⁺) entrenched anodized Ti with hydroxyapatite hybrid nano-sctructure meant for dilapidation of organic contaminant from the environment. The N⁺ was entrenched at 70 keV with varying doses (1 × 10¹⁶, 5 × 10¹⁶, 1 × 10¹⁷ and 2.5 × 10¹⁷ N⁺/cm²) into anodized Ti surface. Functional groups, phase structure, topographic and morphologic characterizations of the synthesized hybrid nano-sctructure were analyzed using Infra Red Spectroscopy, X-ray diffraction and Microscopic techniques, respectively. Wettability of the specimens was found out using contact angle measurements. The anodized Ti specimens without N⁺ have exhibited less surface energy than the specimens with N⁺. Porous shell gets smoothened after the entrenchment of N⁺. Compared to all the doses of nitrogen implantation, better performance was observed for 5 × 10¹⁶ N⁺/cm² dose. Moreover, the samples with N⁺ showed better charge transfer resistance indicating enhanced photocatalytic performance of N⁺ entrenched titania than other samples.

Current Trends in the Utilization of Photolysis and Photocatalysis Treatment Processes for the Remediation of Dye Wastewater: A Short Review

Development in the textile industry leads to an increased demand for the use of various dyes. Moreover, there is the use of some dyes in the food industry as well as medical diagnostics. Thereby, increased demand for dyes in various fields has resulted in dye-containing wastewater. Only a small portion of the generated wastewater is adequately treated. The rest is usually dumped or otherwise directly discharged into the sewage system, which ultimately enters rivers, lakes, and streams. The handling and disposal of such concentrated wastewater, especially the dye-containing wastewater, is considered to be a major environmental issue from the moment of its generation to its ultimate disposal. Conventional water treatment methods such as flotation, filtration, adsorption, etc., are non-destructive physical separation processes. They only transfer the pollutants to other phases, thereby generating concentrated deposits. The advanced oxidation process (AOP) is one of the most effective emerging methods for the treatment of wastewater containing chemical pollutants. The method involves the formation and interaction of highly reactive hydroxyl radicals under suitable activation conditions. These radicals are non-selective and efficient for the destruction and eventual mineralization of recalcitrant organic pollutants. This review aims at the pros and cons of using photocatalysis as an efficient AOP to degrade dye-containing wastewater.

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.

Removal of the Hazardous Congo Red Dye through Degradation under Visible Light Photocatalyzed by C,N Co-Doped TiO2 Prepared from Chicken Egg White

The C,N co-doped TiO2 photocatalyst was prepared by interacting the chicken egg white having various weights (1, 2, and 4 g) with 1 g of TiO2 in an autoclave through the hydrothermal process at 150°C. The C,N co-doped TiO2 photocatalysts were characterized using Fourier transform infrared (FTIR), X-ray diffraction (XRD), specular reflectance UV/visible (SRUV/Vis), and transmission electron microscope (TEM) instruments. The photocatalytic activity of the co-doped TiO2 was evaluated by monitoring the photo-decolorization of Congo red dye under visible light through a batch experiment. The characterization results assigned that the C and N atoms from the chicken egg white have been successfully co-doped into TiO2 through interstitial and substitutional combination, which could notably narrow their band gap energy entering into the visible region. In line with the gap narrowing, the co-doping C,N into TiO2 could remarkably improve the photocatalytic activity under visible light in the dye photo-decolorization. The enhancement of the photocatalyst activity of TiO2-C,N was controlled by the weight of the egg white introduced, and 2 g of the egg white resulted in the highest activity. Further, the best dye photo-decolorization, which was about 98%, of 10 mg/L Congo red dye in 100 mL of the solution under visible irradiation could be reached by applying TiO2-C,N prepared from 2 g of the egg white, within 45 min, at pH 7, and 50 mg of the photocatalyst mass.

A review on recent advancements in photocatalytic remediation for harmful inorganic and organic gases

Due to the continuous increase in industrial pollution and modern lifestyle, several types of air contaminants and their concentrations are emerging in the atmosphere. Besides, photocatalysis has gained much attention in the elimination of air pollution. Several ultraviolet and visible light active photocatalysts were tested in air pollutant treatment and thereby, the number of reports was increased in the past few years. In this context, this review describes the photocatalytic treatment of gaseous inorganic contaminants like NO_x, H₂S, and organic pollutants like formaldehyde, acetaldehyde, and benzene derivatives. Different photocatalysts with their air pollutant removal efficiency were explained. Improving strategies such as metal/non-metal doping, composite formation for photocatalyst activities have been studied. Moreover, an analysis is presented from each of the existing photocatalytic immobilization approaches. Also, factors responsible for effective photocatalysis were explained. Overall, the photocatalytic abatement technique is an auspicious way to eliminate different air contaminants. Besides, existing drawbacks and future challenges are also discussed.

Fabrication and Photocatalytic Properties of Electrospun Fe-Doped TiO2 Nanofibers Using Polyvinyl Pyrrolidone Precursors

For the removal of pollutants, a modified TiO₂ photocatalyst is attracting attention. Fe-doped TiO₂ nanofibers were prepared through a combination of electrospinning and calcination. Morphological characterization of the sample was conducted using field-emission scanning electron and transmission electron microscopy. The crystal structure of each sample was analyzed using high-resolution transmission electron microscopy, selected area electron diffraction, and Fast Fourier Transform imaging. The average diameter of the Fe-doped TiO₂ nanofibers was measured to be 161.5 nm and that of the pure TiO₂ nanofibers was 181.5 nm. The crystal phase when heat treated at 350 °C was anatase for TiO₂ nanofibers and rutile for Fe-doped TiO₂ nanofibers. The crystal phase of the TiO₂ matrix was easily transitioned to rutile by Fe-doping. The photocatalytic performance of each sample was compared via the photodegradation of methylene blue and acid orange 7 under ultraviolet and visible light irradiation. In the Fe-doped TiO₂ nanofibers, photodegradation rates of 38.3% and 27.9% were measured under UV irradiation and visible light, respectively. Although other catalysts were not activated, the photodegradation rate in the Fe-doped TiO₂ nanofibers was 9.6% using acid orange 7 and visible light. For improved photocatalytic activity, it is necessary to study the concentration control of the Fe dopant.

Photocatalysis over N-Doped TiO2 Driven by Visible Light for Pb(II) Removal from Aqueous Media

The photocatalysis process over N-doped TiO2 under visible light is examined for Pb(II) removal. The doping TiO2 with N element was conducted by simple hydrothermal technique and using urea as the N source. The doped photocatalysts were characterized by DRUVS, XRD, FTIR and SEM-EDX instruments. Photocatalysis of Pb(II) through a batch experiment was performed for evaluation of the doped TiO2 activity under visible light, with applying various fractions of N-doped, photocatalyst mass, irradiation time, and solution pH. The research results attributed that N doping has been successfully performed, which shifted TiO2 absorption into visible region, allowing it to be active under visible irradiation. The photocatalytic removal of Pb(II) proceeded through photo-oxidation to form PbO2. Doping N into TiO2 noticeably enhanced the photo-catalytic oxidation of Pb(II) under visible light irradiation. The highest photocatalytic oxidation of 15 mg/L Pb(II) in 25 mL of the solution could be reached by employing TiO2 doped with 10%w of N content 15 mg, 30 min of time and at pH 8. The doped-photocatalyst that was three times repeatedly used demonstrated significant activity. The most effective process of Pb(II) photo-oxidation under beneficial condition, producing less toxic and handleable PbO2 and good repeatable photocatalyst, suggest a feasible method for Pb(II) remediation on an industrial scale.