Carbon and Nitrogen Co-doped TiO2 with Enhanced Visible-Light Photocatalytic Activity

Effect of precursors on carbon dot functionalization and applications: a review

Carbon dots (CDs) are a type of carbon-based nanoparticle (NP) that have risen in popularity due to their unique tuneable physicochemical and optical properties. CDs have received a significant amount of attention in biological based applications due to their low cytotoxicity, stable photoluminescence, and small size. They have demonstrated the ability to retain certain properties from their carbon precursors, enabling NP design via precursor selection. Thus, direct functionalization of a CD can be achieved without the need for post synthesis modification. However, CDs derived from the same class of carbon precursor can also have profoundly variable applications. Indicating that, in conjunction with precursor properties, other functional attributes can be imposed on the CD during the synthesis process to enable cross-cutting applications from a single carbon precursor. Here, we will highlight various CD precursors and the resulting multifunctional CDs, as well as rational design of CDs for specific biological and materials science applications via precursor selection.

Visible light induced photocatalytic degradation of norfloxacin using xC-TiO2

In recent years, antibiotic pollution has become a major environmental concern. The extensive production and widespread use of prescribed antibiotics have significantly impacted ecosystems. The main objective of the present study is to investigate the photocatalytic degradation of the antibiotic norfloxacin (NFX) under visible light. In this work photocatalysis of NFX was demonstrated under the source of visible radiation by using carbon dopped-titania (C-TiO 2 ) nanoparticles as catalyst prepared by a modified sol-gel method using n-hexane and benzene as carbon precursors. The synthesized samples were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and energy dispersive X-ray (EDX) techniques. The effect of various parameters like initial concentration, catalyst dosage, irradiation time, pH, and inorganic ions were investigated on the photocatalysis of NFX. The XRD and SEM analysis exhibits that the synthesized C-TiO 2 nanoparticles were of anatase phase having spherical shape with a mean particle size of about 11-17 nm. The results shows that the best photocatalytic efficiency (74 % & 81 %) was achieved at pH = 8 in 150 min. The degradation of NFX follows pseudo-2nd -order kinetics, while favors Langmuir isotherm model. The inhibition effect of various inorganic ions on the photocatalysis of NFX was in the order of F⁻>SO4 2⁻>HCO3 ⁻>NO3 ⁻. The present study shows that C-TiO 2 is an optimistic and efficient catalyst for the photocatalysis of NFX antibiotics.

Preparation of Red TiO2 with Excellent Visible Light Absorption from Industrial TiOSO4 Solution for Photocatalytic Degradation of Dyes

At present, it is still difficult to significantly reduce the bandgap of TiO2 to promote its visible light absorption. Herein, we first synthesized sulfur-doped TiO2 from industrial TiOSO4 and then successfully synthesized red TiO2 nanoparticles by calcination with the N source melamine. Theoretical calculations show that predoped S could markedly decrease the formation energy and substitution energy of N-doped TiO2, especially in high N/Ti ratios. The red TiO2 nanoparticles have a low bandgap (2.10 eV) and exhibit remarkable visible light absorption capacity. Electron paramagnetic resonance measurements show that the red TiO2 has abundant oxygen vacancies and Ti3+. The synergetic effect of Ti3+, oxygen vacancies, and nonmetallic element doping leads to the bandgap of TiO2 significantly being reduced. In addition, the red TiO2 exhibits great photocatalytic activity in the visible light degradation of rhodamine B (Rh.B) and methylene blue (MB). This study provides a new idea for the preparation of TiO2 with high visible light absorption.

Synergistic effect of adsorption-photocatalytic reduction of Cr(VI) in wastewater with biochar/TiO2 composite under simulated sunlight illumination

Photocatalysis, which is an alternative technology to conventional methods, utilizes solar energy as the driving force to address environmental concerns and has attracted widespread attention from chemists worldwide. In this study, a series of photocatalytic materials composed of agricultural waste and titanium dioxide (TiO2) nanomaterial was prepared for the synergistic adsorption-photocatalytic reduction of hexavalent chromium in wastewater under mild conditions. The results showed that the TiO2 nanomaterial exhibited a higher photogenerated carrier separation efficiency and performance for the adsorption-photocatalytic reduction of Cr(VI) after loading straw biochar (BC). When the loading amount of BC was 0.025 g (i.e., TBC-3), the removal efficiency of Cr(VI) was as high as 99.9% under sunlight irradiation for 25 min, which was 2.9 and 3.5 times higher than that of pure TiO2 and BC samples, respectively. Additionally, after four cycles of experiments, the removal efficiency of Cr(VI) by TBC-3 remained at about 93.0%, proving its good chemical ability in our reaction system. Its excellent adsorption-photocatalytic performance is mainly attributed to the synergistic effect of the strong adsorption of BC and the outstanding photocatalytic performance of TiO2. Finally, the possible mechanism for the synergistic adsorption-photocatalytic reduction on BC/TiO2 to remove the highly toxic Cr(VI) in wastewater was proposed.

Porous Geopolymer/ZnTiO3/TiO2 Composite for Adsorption and Photocatalytic Degradation of Methylene Blue Dye

In this study, GP (geopolymer) and GTA (geopolymer/ZnTiO₃/TiO₂) geopolymeric materials were prepared from metakaolin (MK) and characterized by X-ray diffraction (XRD), X-ray fluorescence (XRF), scanning electron microscopy (SEM), energy dispersive X-rays (EDX), specific surface area (SSA), and point of zero charge (PZC). The adsorption capacity and photocatalytic activity of the compounds prepared in the form of pellets was determined by degradation of the methylene blue (MB) dye in batch reactors, at pH = 7.0 ± 0.2 and room temperature (20 °C). The results indicate that both compounds are highly efficient at adsorbing MB, with an average efficiency value of 98.5%. The Langmuir isotherm model and the pseudo second order kinetic model provided the best fits to the experimental data for both compounds. In the MB photodegradation experiments under UVB irradiation, GTA reached an efficiency of 93%, being higher than that achieved by GP (4%). Therefore, the incorporation of ZnTiO₃/TiO₂ in the geopolymeric matrix allowed GTA to achieve higher overall efficiency, by combining adsorption and photocatalysis, compared to the GP compound. The results indicate that the synthesized compounds could be used for up to five consecutive cycles for the removal of MB from wastewater through adsorption and/or photocatalysis processes.

Sputter -coated N-enriched mixed metal oxides (Ta2O5-Nb2O5-N) composite: A resilient solar driven photocatalyst for water purification

This study demonstrated the formation of N-enriched mixed metal oxides (Ta₂O₅-Nb₂O₅-N and Ta₂O₅-Nb₂O₅) thin film composites used as photocatalysts to degrade P-Rosaniline Hydrochloride (PRH-Dye) dye under solar radiation. By controlling the N gas flow rate during the sputtering process, the N concentration in the Ta₂O₅-Nb₂O₅-N composite is significantly included, and demonstrated by XPS and HRTEM analysis. With the help of XPS and HRTEM investigations, it was determined that the addition of N to Ta₂O₅-Nb₂O₅-N significantly enhances the active sites. The Ta-O-N bond (N 1 s and Ta 4p_3/2 spectra) was verified by the XPS spectra. Ta₂O₅-Nb₂O₅ was found to have a lattice interplanar distance (d-spacing) of 2.52, whereas Ta₂O₅-Nb₂O₅-N showed the 2.5 (620 planes). A sputter-coated Ta₂O₅-Nb₂O₅and Ta₂O₅-Nb₂O₅-N photocatalysts were prepared, and their photocatalytic activity was evaluated using PRH-Dye as a model pollutant under solar radiation by adding H₂O₂ (0.01 mol). The photocatalytic activity of the Ta₂O₅-Nb₂O₅-N composite was compared with TiO₂ (P-25) and Ta₂O₅-Nb₂O₅. Ta₂O₅-Nb₂O₅-N showed very high photocatalytic activity compared to Degussa P-25 TiO₂ and Ta₂O₅-Nb₂O₅ under solar radiation and confirmed the presence of N in Ta₂O₅-Nb₂O₅-N significantly increased the generation of ˙OH radicals (in pH 3, 7 and 9). With the use of LC/MS, the stable intermediates or metabolite created during the photooxidation of PRH-Dye were assessed. The results of this study will provide useful insights on how Ta₂O₅-Nb₂O₅-N influences the efficiency of water pollution remediation.

C,N co-doped TiO2 hollow nanofibers coated stainless steel meshes for oil/water separation and visible light-driven degradation of pollutants

Complex pollutants are discharging and accumulating in rivers and oceans, requiring a coupled strategy to resolve pollutants efficiently. A novel method is proposed to treat multiple pollutants with C,N co-doped TiO₂ hollow nanofibers coated stainless steel meshes which can realize efficient oil/water separation and visible light-drove dyes photodegradation. The poly(divinylbenzene-co-vinylbenzene chloride), P(DVB-co-VBC), nanofibers are generated by precipitate cationic polymerization on the mesh framework, following with quaternization by triethylamine for N doping. Then, TiO₂ is coated on the polymeric nanofibers via in-situ sol-gel process of tetrabutyl titanate. The functional mesh coated with C,N co-doped TiO₂ hollow nanofibers is obtained after calcination under nitrogen atmosphere. The resultant mesh demonstrates superhydrophilic/underwater superoleophobic property which is promising in oil/water separation. More importantly, the C,N co-doped TiO₂ hollow nanofibers endow the mesh with high photodegradation ability to dyes under visible light. This work draws an affordable but high-performance multifunctional mesh for potential applications in wastewater treatment.

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.

Study of synergistic effect of cobalt and carbon codoped with TiO2 photocatalyst for visible light induced degradation of phenol

In this work, we reported synthesis of cobalt and carbon codoped TiO₂ (Co-C-TiO₂) nanoparticles were prepared using co-precipitation technique. The synthesized catalysts are analyzed by various methods. The powder XRD pattern confirmed that all the samples were polycrystalline of anatase phase and particle size of resultant nanoparticle was reduced correlated with bare TiO₂ sample. FTIR measurements exhibit the identification of functional groups present at the surface of TiO₂. FESEM micrograph showed that the shape of codoped TiO₂ nanoparticles are approximately sphere. The attained energy gap of Co doped and C codoping of TiO₂ modifies to a level below the energy gap of TiO₂ anatase specifying a high capability to absorb visible light. The recombination rate of photo-induced electrons and holes for Co-C codoped TiO₂ nanoparticles is significantly reduced. The synthesized samples are assessed in degradation of phenol by the illumination of visible light. The results confirmed that photocatalytic activity enhanced due to doping and codoping of Co and C. As a result, Co-C codoped TiO₂ nanoparticles exhibited a higher visible-light photocatalytic activity in compared with Co-TiO₂ and bare TiO₂ with the maximum degradation efficiency of 98, 75 and 15%, respectively. And also, the reusability of the catalyst was proved when 95% degradation could be achieved after consecutive batches. It is predictable that this work will provide new insights to increase the visible light active photocatalysts for environmental problems.

Investigation on the gaseous benzene removed by photocatalysis employing TiO2 modified with cobalt and iodine as photocatalysts under visible light

A new type of photocatalysts, nanocrystalline titanium dioxide (TiO₂) doped with Co and I, were synthesized and modified via the sol-gel method to enhance the utilization of visible light. Herein, mono- and co-doped TiO₂ (i.e. Co-TiO₂, I-TiO₂, Co-I-TiO₂) were employed as the photocatalysts to investigate the photocatalytic performance on gaseous benzene removal. The prepared photocatalysts were characterized by X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET)-specific surface areas, Raman spectroscopy, UV-visible diffuse reflectance spectroscopy (UV-vis-DRS), X-ray photoelectron spectroscopy (XPS), photoluminescence (PL), and electrochemical impedance spectroscopy (EIS). Results indicated that both particle sizes and band gaps of TiO₂ were significantly reduced by doping with Co/I. Also, the lattice defects and the specific surface areas of TiO₂ were substantially augmented by adding Co/I because of the increase of oxygen vacancies, especially for Co-I-TiO₂. Meanwhile, Co and I were distributed on the titanium base with the existence of multivalent states. The benzene treatment capacity of Co-I-TiO₂, Co-TiO₂, I-TiO₂ and Pure TiO₂ is 441.46, 424.36, 388.06, and 51.25 μgC₆H₆/(g·h), respectively. To sum up, photocatalytic degradation of gaseous benzene could be improved by doping with Co/I because of the extension of catalyst lifetime and light response range covering visible light.

Visible-Light Driven Photodegradation of Industrial Pollutants Using Nitrogen-Tungsten Co-Doped Nanocrystalline TiO2: Spectroscopic Analysis of Degradation Reaction Path

The purpose to conduct this research work is to study the effect of photocatalytic degradation by developing cost-effective and eco-friendly nitrogen and tungsten (metal/non-metal) co-doped titania (TiO₂). The inherent characteristics of synthesized nanoparticles (NPs) were analyzed by Fourier transform infra-red spectroscopy (FT-IR), ultra-violet visible (UV-Vis) spectroscopy, Raman spectroscopy, Field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDX), dynamic light scattering (DLS), X-ray diffraction (XRD) spectrometry, and atomic force microscopy (AFM). Co-doping of metal and non-metal has intensified the photocatalysis trait of TiO₂ nanoparticles in an aqueous medium. This co-doping of transition metal ions and modification of nitrogen extended the absorption into the visible region subsequently restraining the recombination of electrons/holes pair. The stronger light absorption in the visible region was required for the higher activity of photodegradation of dye under visible light illumination to confine bandgap energy which results in accelerating the rate of photodegradation. After efficient doping, the bandgap of titania reduced to 2.38 eV and caused the photodegradation of malachite green in visible light. The results of photocatalytic degradation were confirmed by using UV/Vis. spectroscopy and high-performance liquid chromatography coupled with a mass spectrophotometer (HPLC-ESI-MS) was used for the analysis of intermediates formed during photocatalytic utility of the work.

Sustainable vs. Conventional Approach for Olive Oil Wastewater Management: A Review of the State of the Art

The main goal of this review is to collect and analyze the recently published research concerning the conventional and sustainable treatment processes for olive mill wastewater (OMW). In the conventional treatment processes, it is noticed that the main objective is to meet the environmental regulations for remediated wastewater without considering the economical values of its valuable constituents such as polyphenols. These substances have many important environmental values and could be used in many vital applications. Conversely, sustainable treatment processes aim to recover the valuable constituents through different processes and then treat the residual wastewater. Both approaches’ operational and design parameters were analyzed to generalize their advantages and possible applications. A valorization-treatment approach for OMW is expected to make it a sustainable resource for ingredients of high economical value that could lead to a profitable business. In addition, inclusion of a recovery process will detoxify the residual OMW, simplify its management treatment, and allow the possible reuse of the vast amounts of processed water. In a nutshell, the proposed approach led to zero waste with a closed water cycle development.

Enhancing the physical properties and photocatalytic activity of TiO2 nanoparticles via cobalt doping

Cobalt-doped TiO₂-based diluted magnetic semiconductors were successfully synthesized using a co-precipitation method. The X-ray diffraction study of all the samples showed good crystallinity, matching the standard tetragonal anatase phase. The X-ray diffraction peaks of the cobalt-doped sample slightly shifted towards a lower angle showing the decrease in particle size and distortion in the unit cell due to cobalt incorporation in the lattice of TiO₂. Transmission electron microscopy showed the spherical morphology of the TiO₂ nanoparticles, which decreased with Co-doping. The optical characteristics and band gap investigation revealed that defects and oxygen vacancies resulted in lower band gap energy and maximum absorption in the visible region. Dielectric measurements showed enhancement in the dielectric constant and AC conductivity, while the dielectric loss decreased. The enhancement in the dielectric properties was attributed to interfacial polarization and charge carrier hopping between Co and Ti ions. The magnetic properties displayed that pure TiO₂ was diamagnetic, while Co-doped TiO₂ showed a ferromagnetic response at 300 K. The visible light-driven photocatalytic activity showed an improvement for Co-doped TiO₂. Our results demonstrate that Co-doping can be used to tune the physical properties and photocatalytic activity of TiO₂ for possible spin-based electronics, optoelectronics, and photo-degradation applications.

(a) dielectric constant, (b) dielectric loss and (c) AC conductivity vs. frequency for un-doped and 5 at% Co-doped TiO₂ NPs.

Nano Metal-Containing Photocatalysts for the Removal of Volatile Organic Compounds: Doping, Performance, and Mechanisms

Volatile organic compounds (VOCs) in indoor air are considered a major threat to human health and environmental safety. The development of applicable technologies for the removal of VOCs is urgently needed. Nowadays, photocatalytic oxidation (PCO) based on metal-containing photocatalysts has been regarded as a promising method. However, unmodified photocatalysts are generally limited in applications because of the narrow light response range and high recombination rate of photo-generated carriers. As a result, nano metal-containing photocatalysts doped with elements or other materials have attracted much attention from researchers and has developed over the past few decades. In addition, different doping types cause different levels of catalyst performance, and the mechanism for performance improving is also different. However, there are few reviews focusing on this aspect, which is really important for catalyst design and application. This work aims to give a comprehensive overview of nano metal-containing photocatalysts with different doping types for the removal of VOCs in an indoor environment. First, the undoped photocatalysts and the basic mechanism of PCO is introduced. Then, the application of metal doping, non-metal doping, co-doping, and other material doping in synthetic metal-containing photocatalysts are discussed and compared, respectively, and the synthesis methods, removal efficiency, and mechanisms are further investigated. Finally, a development trend for using nano metal-containing photocatalysts for the removal of VOCs in the future is proposed. This work provides a meaningful reference for selecting effective strategies to develop novel photocatalysts for the removal of VOCs in the future.

Preparation of a Photosensitive Composite Carbon Fiber for Spilled Oil Cleaning

This paper deals with preparing a functional composite carbon fiber with a large surface area for spilled oil cleaning. The composite fiber consisted of photosensitive oxide particles and polymer-derived carbon. It was made by co-spinning the polymer and metallic compounds. After heat treatment at high temperatures, an activated carbon fiber containing oxide particles was obtained. The particles were found distributed in the fiber and at the surface of the fiber. The composite fiber was found sensitive to sunlight. Fiber mats made of the composite fiber possessed a high surface area for oil absorption and removal. Cobalt(II) titanate particles were obtained from the reaction of titanium dioxide and cobalt oxide. The reaction happened in situ through the hydrolysis of metallic compounds in the spun fiber. The titanium dioxide and cobalt(II) titanate particle-containing fibers demonstrated the photoactivity in the visible light spectrum. It was concluded that particle-containing composite carbon fiber mats can be prepared successfully by co-electrospinning. Due to the oleophilic property and the high active surface area, the composites are suitable for spilled oil cleaning through fast absorption.

Hydrogenation of furfural to furfuryl alcohol over MOF-derived Fe/Cu@C and Fe3O4/Cu@C catalysts

With Cu-MOF-loaded Fe(NO3)3 as the precursor (Fe(NO3)3/Cu-MOF), Fe/Cu@C and Fe3O4/Cu@C catalysts were prepared from heating under the H2 and N2 atmosphere, respectively. When Fe(NO3)3/Cu-MOF was heated under different atmospheres, Cu-MOF...

Oxygen-containing groups and P doped porous carbon nitride nanosheets towards enhanced photocatalytic activity

Metal-free polymer graphite carbon nitride (CN) is a promising photocatalyst that has garnered significant research attention. However, unmodified CN possesses several shortcomings such as low specific surface area, poor dispersibility in water, and rapid photogenerated electron-hole recombination, which have severely impacted its mass adoption. Here, this study proposed a two-step heat treatment method to incorporate P dopant and the containing-oxygen groups successively into CN. The final product, denoted as PO-CN, possessed a porous ultrathin nanosheet-like morphology. The introduction of P dopant altered the intrinsic electronic structure of CN. Meanwhile, the presence of oxygen-containing groups improved the dispersibility of PO-CN in water. Also, it led to the formation of a porous ultrathin structure that could provide more active sites. Through the synergistic effects of these two methods, PO-CN demonstrated superior photocatalytic performance compared to the unmodified counterpart. Based on the collective results obtained experimentally and theoretically, PO-CN possessed a porous ultrathin structure, low resistance, and low carrier recombination. The results show an optimal hydrogen evolution rate of PO-CN (997.7 mol h^-1 g^-1), which was 11.2 times and 3.22 times that of the CN (88.89 mol h^-1 g^-1) and PCN (310.3 mol h^-1 g^-1). Moreover, PO-CN was then used in the degradation of Rhodamine B, and a degradation kinetic constant (k) of 0.15009 was calculated, which was 18.42 times and 8.22 times higher as compared to those of CN (0.00815) and PCN (0.01826). Hence, this work provides a new strategy for the alteration of the morphology and electronic structure of CN.

Recent advances in photocatalytic remediation of emerging organic pollutants using semiconducting metal oxides: an overview

Many untreated and partly treated wastewater from the home and commercial resources is being discharged into the aquatic environment these days, which contains numerous unknown and complex natural and inorganic compounds. These compounds tend to persist, initiating severe environmental problems, which affect human health. Conventionally, physicochemical treatment methods were adopted to remove such complex organic chemicals, but they suffer from critical limitations. Over time, photocatalysis, an advanced oxidation process, has gained its position for its efficient and fair performance against emerging organic pollutant decontamination. Typically, photocatalysis is a green technology to decompose organics under UV/visible light at ambient conditions. Semiconducting nanometal oxides have emerged as pioneering photocatalysts because of large active surface sites, flexible oxidation states, various morphologies, and easy preparation. The current review presents an overview of emerging organic pollutants and their effects, advanced oxidation processes, photocatalytic mechanism, types of photocatalysts, photocatalyst support materials, and methods for improving photodegradation efficiency on the degradation of complex emerging organic pollutants. In addition, the recent reports of metal-oxide-driven photocatalytic remediation of emerging organic pollutants are presented in brief. This review is anticipated to reach a broader scientific community to understand the first principles of photocatalysis and review the recent advancements in this field.

La-Doped ZnTiO3/TiO2 Nanocomposite Supported on Ecuadorian Diatomaceous Earth as a Highly Efficient Photocatalyst Driven by Solar Light

Currently, there is great interest in the use of TiO2 for photocatalytic remediation of wastewater. Doping, heterojunction, and immobilization on porous materials are effective methods to improve the photocatalytic efficiency of this semiconductor oxide. In this study, ZnTiO3/TiO2 (ZTO) and ZnTiO3/TiO2/La (ZTO/La) nanocomposites were successfully prepared and immobilized on diatomaceous earth (DE). The composition and texture of the composites prepared were characterized by X-ray diffraction (XRD), X-ray fluorescence (XRF), diffuse reflectance spectroscopy (DRS), scanning electron microscopy (SEM-EDX), and specific surface area (SSA). The adsorption capacity and photocatalytic activity of the composites were determined via degradation of methylene blue (MB) in batch reactors. The materials evaluated were prepared in the shape of 0.2 cm (diameter) and 1.0 cm (length) cylindrical extrudates. The results indicate that the ZTO/La-DE composite exhibited higher efficiency for the removal of MB under solar irradiation than both ZTO-DE and DE. The pseudo-second-order model and the Langmuir isotherm model were better suited to explain the adsorption process. The highest degradation percentage of MB obtained was 96% after 150 min of irradiation. The results indicate that synthesized composite could be used for the removal of cationic dyes in wastewater.

Synthesis and Characterization of Iron-Doped TiO2 Nanoparticles Using Ferrocene from Flame Spray Pyrolysis

Iron-doped titanium dioxide nanoparticles, with Fe/Ti atomic ratios from 0% to 10%, were synthesized by flame spray pyrolysis (FSP), employing a single-step method. Ferrocene, being nontoxic and readily soluble in liquid hydrocarbons, was used as the iron source, while titanium tetraisopropoxide (TTIP) was used as the precursor for TiO2. The general particle characterization and phase description were examined using ICP-OES, XRD, BET, and Raman spectroscopy, whereas the XPS technique was used to study the surface chemistry of the synthesized particles. For particle morphology, HRTEM with EELS and EDS analyses were used. Optical and magnetic properties were examined using UV–vis and SQUID, respectively. Iron doping to TiO2 nanoparticles promoted rutile phase formation, which was minor in the pure TiO2 particles. Iron-doped nanoparticles exhibited a uniform iron distribution within the particles. XPS and UV–vis results revealed that Fe2+ was dominant for lower iron content and Fe3+ was common for higher iron content and the iron-containing particles had a contracted band gap of ~1 eV lower than pure TiO2 particles with higher visible light absorption. SQUID results showed that doping TiO2 with Fe changed the material to be paramagnetic. The generated nanoparticles showed a catalytic effect for dye-degradation under visible light.

C-,N- and S-Doped TiO2 Photocatalysts: A Review

This article presents an overview of the reports on the doping of TiO2 with carbon, nitrogen, and sulfur, including single, co-, and tri-doping. A comparison of the properties of the photocatalysts synthesized from various precursors of TiO2 and C, N, or S dopants is summarized. Selected methods of synthesis of the non-metal doped TiO2 are also described. Furthermore, the influence of the preparation conditions on the doping mode (interstitial or substitutional) with reference to various types of the modified TiO2 is summarized. The mechanisms of photocatalysis for the different modes of the non-metal doping are also discussed. Moreover, selected applications of the non-metal doped TiO2 photocatalysts are shown, including the removal of organic compounds from water/wastewater, air purification, production of hydrogen, lithium storage, inactivation of bacteria, or carbon dioxide reduction.

A TiO2 Coated Carbon Aerogel Derived from Bamboo Pulp Fibers for Enhanced Visible Light Photo-Catalytic Degradation of Methylene Blue

Carbon aerogels (CA) derived from bamboo cellulose fibers were coupled with TiO2 to form CA/TiO2 hybrids, which exhibited extraordinary performance on the photo-catalytic degradation of methylene blue (MB). The structure and morphology of CA/TiO2 were characterized by field emission scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and Raman spectrum. The CA displayed a highly porous and interconnected three-dimensional framework structure, while introducing the catalytic active sites of TiO2 onto the aerogel scaffold could remarkably enhance its photo-catalytic activity. The adsorption and photo-catalytic degradation of MB by the CA/TiO2 hybrid were investigated. The maximum adsorption capacity of CA/TiO2 for MB was 18.5 mg/g, which outperformed many similar materials reported in the literature. In addition, compared with other photo-catalysts, the present CA/TiO2 demonstrated superior photo-catalytic performance. Almost 85% of MB in 50 mL solution with a MB concentration of 10 mg/L could be effectively degraded by 15 mg CA/TiO2 in 300 min.

Fe- and Mn-modified SO42−/ZrO2 conjoined O2–Ac2O as a composite catalytic system for highly selective nitration of 1-nitronaphthalene with NO2 to valuable 1,5-dinitronaphthalene

NO2 as benign nitrating agent and Fe–Mn bimetallic modified SZ as catalyst replaced traditional nitric–sulfuric mixed acid systems for 1-NN nitration. The synergism of Fe1.5Mn0.5–SZ and O2–Ac2O significantly improved the selectivity to 1,5-DNN.

Nitrogen Doping and Carbon Coating Affects Substrate Selectivity of TiO2 Photocatalytic Organic Pollutant Degradation

A series of carbon-coated, nitrogen-doped titanium dioxide photocatalysts was produced and characterized. N-doped TiO₂ powder samples were prepared using a sol-gel method and subsequently used for making doped-TiO₂ thin films on glass substrates. Carbon layers were coated on the films by a thermal decomposition method using catechol. Diffuse reflectance spectra and Mott-Schottky analyses of the samples proved that nitrogen doping and carbon coating can slightly lower the band gap of TiO₂ , broaden its absorption to visible light and enhance its n-type character. According to photocatalytic tests against model contaminants, carbon-coated nitrogen-doped TiO₂ films have better performance than simple TiO₂ on the degradation of Rhodamine B dye molecules, but are poorly effective for degrading 4-chlorophenol molecules. Several possible explanations are proposed for this result, supported by scavenging experiments. This reveals the importance of a broad substrate scope when assessing new photocatalytic materials for water treatment, something which is often overlooked in many literature studies.

Photocatalytic degradation of microcystin-LR by modified TiO2 photocatalysis: A review

Microcystin-LR (MC-LR), the most toxic and commonly encountered cyanotoxin, is produced by harmful cyanobacterial blooms and potentially threatens human and ecosystems health. Titanium dioxide (TiO₂) photocatalysis is attracting growing attention and has been considered as an efficient, environmentally friendly and promising solution to eliminate MC-LR in the aquatic ecosystems. Over recent decades, scientific efforts have been directed towards the understanding of fundamentals, modification strategies, and application potentials of TiO₂ photocatalysis in degrading MC-LR. In this article, recent reports have been reviewed and progress has been summarized in the development of heterogeneous TiO₂-based photocatalysts for MC-LR photodegradation under visible, UV, or solar light. The proposed photocatalytic principles of TiO₂ and destruction of MC-LR have been thoroughly discussed. Specifically, some main modification methods for improving the drawbacks and performance of TiO₂ nanoparticle were highlighted, including element doping, semiconductor coupling, immobilization, floatability amelioration and magnetic separation. Moreover, the performance evaluation metrics quantum yield (QY) and figure of merit (FOM) were used to compare different photocatalysts in MC-LR degradation. The best performance was seen in N-TiO₂ with QY and FOM values of 2.20E-07 molecules/photon and 1.00E-11 mol·L/(g·J·h). N-TiO₂ or N-TiO₂-based materials may be excellent options for photocatalyst design in terms of MC-LR degradation. Finally, a summary of the remaining challenges and perspectives on new tendencies in this exciting frontier and still an emerging area of research were addressed accordingly. Overall, the present review will offer a deep insight for understanding the photodegradation of MC-LR with modified TiO₂ to further inspire researchers that work in associated fields.

Sol-gel synthesis of carbon-doped TiO2 nanoparticles based on microcrystalline cellulose for efficient photocatalytic degradation of methylene blue under visible light

Carbon-doped titanium dioxide photocatalyst with improved performance in visible light was prepared via the typical sol-gel method. Microcrystalline cellulose (MCC) was used as carbon elements source. The prepared pure and carbon-doped TiO₂ samples were calcined at 400-650°C in air and the effect of annealing temperature on the stability of carbon ions was investigated. EDX analysis showed the presence of 5.66 wt.% carbon atoms in TiO₂ nanoparticles formed on MCC, which was attributed to the doping of carbon atoms in TiO₂ lattice. Carbon doping was also confirmed by Raman spectroscopy. According to the UV-VIS DRS analysis, the band gap of TiO₂ particles decreased from 2.96 to 2.71 eV in pure and carbon-doped TiO₂, respectively. Therefore the visible light absorbance increased to 15.05% compared to 0% absorbance in pure TiO₂. The heat treatment of carbon-doped TiO₂ nanostructures showed that carbon element could escape from the O-Ti-O lattice at temperatures higher than 600°C. According to the SEM images, synthesis of TiO₂ in presence of MCC also limited the growth of TiO₂ nanoparticles and controlled the morphology and aggregation of nanoparticles. Carbon doping improved the photocatalytic performance of TiO₂ photocatalyst compared to the pure nanoparticles in degradation of methylene blue in the aqueous phase. Carbon-doped TiO₂ attained the efficiency of 56.25%, 51.18% and 62.95% under UV, visible and solar lights, respectively, compared to 28.43%, 6.36% and 33.65% related to the pure TiO₂.

Studies on interstitial carbon doping from a Ti precursor in a hierarchical TiO2 nanostructured photoanode by a single step hydrothermal route

Carbon doping from a Ti precursor in TiO₂ synthesized by a hydrothermal method was studied. The structural, optical and morphological study of the deposited material was carried out using X-ray diffraction, UV-vis spectroscopy and scanning electron microscopy characterization techniques. The elemental composition of the TiO₂ deposited with different precursor concentrations was studied using X-ray photoelectron spectroscopy and electron dispersive X-ray spectroscopy. The amount of elemental carbon in the TiO₂ matrix is found to be increased as the Ti precursor concentration is increased, which strengthens the proposed idea of carbon doping via a Ti precursor.

Interstitial carbon doping is possible directly from a Ti precursor (titanium(iv) isopropoxide) without using any other carbon source.

Modified Nano-TiO2 Based Composites for Environmental Photocatalytic Applications

TiO2 probably plays the most important role in photocatalysis due to its excellent chemical and physical properties. However, the band gap of TiO2 corresponds to the Ultraviolet (UV) region, which is inactive under visible irradiation. At present, TiO2 has become activated in the visible light region by metal and nonmetal doping and the fabrication of composites. Recently, nano-TiO2 has attracted much attention due to its characteristics of larger specific surface area and more exposed surface active sites. nano-TiO2 has been obtained in many morphologies such as ultrathin nanosheets, nanotubes, and hollow nanospheres. This work focuses on the application of nano-TiO2 in efficient environmental photocatalysis such as hydrogen production, dye degradation, CO2 degradation, and nitrogen fixation, and discusses the methods to improve the activity of nano-TiO2 in the future.

Carbon Black-Doped Anatase TiO2 Nanorods for Solar Light-Induced Photocatalytic Degradation of Methylene Blue

In this work, C-doped TiO₂ nanorods were synthesized through doping carbon black into hydrothermally synthesized solid-state TiO₂ nanowires (NWs) via calcination. The effects of carbon content on the morphology, phase structure, crystal structure, and photocatalytic property under both UV and solar light by the degradation of methylene blue (MB) were explored. Besides, the photoelectrochemical property of C-TiO₂ was systematically studied to illustrate the solar light degradation mechanism. After doping with C, TiO₂ NWs were reduced into nanorods and the surface became rough with dispersed particles. Results showed that C has successfully entered the TiO₂ lattice, resulting in the lattice distortion, reduction of band gap, and the formation of C-Ti-O, which expands TiO₂ to solar light activation. Comparing with P25 and anatase TiO₂ NWs, doping with carbon black showed much higher UV light and solar light photocatalytic activity. The photocatalytic activity was characterized via the degradation of MB, showing that K _ap was 0.0328 min^-1 under solar light, while 0.1634 min^-1 under UV irradiation. The main free radicals involved in methylene blue degradation are H⁺ and OH^•-. Doping with carbon black led to the reduction of photocurrent in a long-term operation, while C-doping reduced the electron-hole recombination and enhanced the carrier migration.

Ultra-Highly Efficient Removal of Methylene Blue Based on Graphene Oxide/TiO2/Bentonite Sponge

An ultra-highly efficient Graphene Oxide/TiO₂/Bentonite (GO/TiO₂/Bent) sponge was synthesized using an in situ hydrothermal method. GO/TiO₂/Bent sponge with a GO mass concentration of 10% exhibited the highest treatment efficiency of methylene blue (MB), combining adsorption and photocatalytic degradation, and achieved a maximum removal efficiency of 100% within about 70 min. To further prove the ultra-high removal capacity of the sponge, the concentration of MB in water increased to ten times the original concentration. At so high a MB concentration, the removal rate was still as high as 80% in 90 min. The photocatalytic mechanism of GO/TiO₂/Bent sponge was discussed through XPS, PL and radicals quenching experiments. Here Bent can immobilize TiO₂ and react with a photo-generated hole to increase the amount of hydroxyl radical; effectively enhancing the degradation of MB.GO sponge enlarges the sensitivity range of TiO₂ to visible light by increasing the charge separation of TiO₂ and reducing the recombination of photo-generated electron–hole pairs. Additionally, GO sponge with an interconnected porous structure provides an effective platform to immobilize TiO₂/bent and makes them be easily recovered. The as-prepared sponge develops a simple and cost-effective strategy to realize the ultra-highly efficient treatment of dyes in wastewater.

Recent Progress in Biochar-Based Photocatalysts for Wastewater Treatment: Synthesis, Mechanisms, and Applications

Biochar (BC) is a carbon-rich material produced from pyrolysis of biomass. In addition to its low toxicity, environmental compatibility, and low cost, BC has the desired advantages of well-developed mesoporous structure and abundant surface functional groups. In recent years, BC-based photocatalysts (BCPs) have played a significant role in many environmental fields. In this paper, we highlight the current progress and several exciting results of BCPs by focusing on their synthesis, characterization, mechanisms, and applications in wastewater treatment. Details on various preparation methods include sol–gel, hydrothermal/solvothermal, ultrasound, calcination, and in situ methods are summarized and discussed. The underlying mechanisms and the applications of BCPs for different semiconductors are reviewed. Furthermore, some future trends and potentials are outlined.

TiO2@C core@shell nanocomposites: A single precursor synthesis of photocatalyst for efficient solar water treatment

This study reports the facile synthesis of highly photoactive TiO₂@C core@shell nanocomposites through a single alkoxide precursor. TiO₂ and carbon-based hybrid nanomaterials are popular photocatalysts owing to their abundance, low toxicity, and high stability, making them strong candidates for practical solar water-treatment applications. However, synthesis of such nanomaterials is often a multi-step process and requires careful control of the external carbon source for producing the desired morphology. In this regard, this study reports the synthesis of well-dispersed TiO₂@C nanocomposites without the need of an external carbon source. The resulting photocatalyst was employed for treatment of various water-borne pollutants including several dyes, pharmaceuticals, and pathogens. Rapid mineralization of pollutants could be achieved even with low amounts of catalyst, with the performance well exceeding that of pristine TiO₂ and P25 Degussa. Results indicate that incorporation of C increases visible-light absorption and greatly improves the separation of photogenerated charge carriers. Given the facile synthesis and the wide scope of operation, the proposed catalyst could be a significant step towards practical photocatalytic solar water-treatment.

Effect of iron doped titanium oxide encapsulated in alginate on photocatalytic activity for the removal of dye pollutants

Iron oxide/titania oxide are encapsulated in alginate biopolymer. These bio-nanocomposites are suitable for the photodegradation of dissimilar organic pollutants under UV irradiation as well as visible light.

Clay-supported anisotropic Au-modified N,S-doped TiO2 nanoparticles for enhanced photocatalytic dye degradation and esterification reactions

Kaolinite clay supported doped TiO₂ and anisotropic gold deposited visible light induced plasmonic nanocatalysts for dye degradation and esterification reactions.

Synthesis and Characterization of Ag@C-TiO2 Nanocomposite for Degradation of Sasirangan Textile Wastewater

Carbon-titanium oxide nanocomposite (denoted as @C-TiO2) was successfully synthesized via hydrothermal method at 150°C for 24 h. The C-TiO2 nanocomposite was furtherly modified by adding an Ag metal dopant (denoted as Ag@C-TiO2) to improve and applied to the photocatalytic degradation of Sasirangan textile wastewater. The composite photocatalysts were characterized by XRD and UV–Vis DRS spectroscopies. XRD patterns showed that TiO2 in @C-TiO2 mainly consisted of a brookite phase, as indicated by a series sharp diffraction peak at 2θ = 27.2° (111), 31.5° (121) and 55.9° (241). The calculated band gap energy (Eg) derived from UV-Vis DRS spectra for TiO2, @C-TiO2, and Ag@C-TiO2 were 2.95 eV, 2.54 eV, and 2.74 eV, respectively. Ag@C-TiO2 photocatalyst was found to be active for the photocatalytic degradation of Sasirangan textile wastewater, as indicated by the change of wastewater color from dark to clear. The quantitative photocatalytic activity of Ag@C-TiO2 was evaluated in the degradation of methylene blue, whereas the conversion of methylene blue was 41.3%. The addition of Ag to @C-TiO2 is believed to play an essential role in the enhancement of photocatalytic activity.