Enhanced photocatalytic degradation of organic pollutants by Ag-TiO2 loaded cassava stem activated carbon under sunlight irradiation

Ag-doped TiO₂ and Ag-doped TiO₂ loaded cassava stem activated carbon (Ag: TiO₂/CSAC) were prepared by sol-gel method and are labelled as AT and AT/CSAC respectively. XRD results confirmed that the anatase-TiO₂ and crystalline size are decreased (12.37 nm) through the silver doping and cassava stem activated carbon loading. UV-Vis showed that the AT/CSAC makes a red shift from the absorption edge compared to pure and AT samples and then the band gap is reduced (2.81 eV). The increased surface area (238.51 m²/g) of the AT/CSAC sample through the Ag and CSAC, respectively. The consequences point out that the highest photodegradation efficiency (98.08%) of the TiO₂ upon silver doping and cassava stem activated carbon loading samples were brilliant green (BG) under sunlight irradiation.

N-Doped Graphene Quantum Dots/Titanium Dioxide Nanocomposites: A Study of ROS-Forming Mechanisms, Cytotoxicity and Photodynamic Therapy

Titanium dioxide nanoparticles (TiO2 NPs) have been proven to be potential candidates in cancer therapy, particularly photodynamic therapy (PDT). However, the application of TiO2 NPs is limited due to the fast recombination rate of the electron (e-)/hole (h+) pairs attributed to their broader bandgap energy. Thus, surface modification has been explored to shift the absorption edge to a longer wavelength with lower e-/h+ recombination rates, thereby allowing penetration into deep-seated tumors. In this study, TiO2 NPs and N-doped graphene quantum dots (QDs)/titanium dioxide nanocomposites (N-GQDs/TiO2 NCs) were synthesized via microwave-assisted synthesis and the two-pot hydrothermal method, respectively. The synthesized anatase TiO2 NPs were self-doped TiO2 (Ti3+ ions), have a small crystallite size (12.2 nm) and low bandgap energy (2.93 eV). As for the N-GQDs/TiO2 NCs, the shift to a bandgap energy of 1.53 eV was prominent as the titanium (IV) tetraisopropoxide (TTIP) loading increased, while maintaining the anatase tetragonal crystal structure with a crystallite size of 11.2 nm. Besides, the cytotoxicity assay showed that the safe concentrations of the nanomaterials were from 0.01 to 0.5 mg mL-1. Upon the photo-activation of N-GQDs/TiO2 NCs with near-infrared (NIR) light, the nanocomposites generated reactive oxygen species (ROS), mainly singlet oxygen (1O2), which caused more significant cell death in MDA-MB-231 (an epithelial, human breast cancer cells) than in HS27 (human foreskin fibroblast). An increase in the N-GQDs/TiO2 NCs concentrations elevates ROS levels, which triggered mitochondria-associated apoptotic cell death in MDA-MB-231 cells. As such, titanium dioxide-based nanocomposite upon photoactivation has a good potential as a photosensitizer in PDT for breast cancer treatment.

Research Progress of Adsorption and Photocatalysis of Formaldehyde on TiO2/AC

Based on the increasingly serious formaldehyde pollution, effective degradation of formaldehyde has become a practical problem that humans urgently need to solve. Among many treatment methods, activated carbon has the advantages of large specific surface area, high adsorption efficiency, and uniform pore size distribution. As a kind of clean photocatalytic material for formaldehyde degradation, titanium dioxide supported by activated carbon has become a research hotspot to develop adsorption-catalytic materials for formaldehyde degradation. In this paper, the research progress of activated carbon and its modification, the photocatalytic principle and modification of titanium dioxide, and TiO2/AC materials are reviewed. The results show that the pore size distribution gradient and acidic oxygen-containing functional groups of activated carbon play key roles in the formaldehyde adsorption process. TiO2 doped with metal ions and nonmetal ions can significantly improve the photocatalytic activity. The TiO2/AC material can greatly improve the photocatalytic rate and achieve the technical goal of efficient and clean degradation for formaldehyde.

Degradation of amoxicillin with sono, photo, and sonophotocatalytic oxidation under low-frequency ultrasound and visible light

The presence of pharmaceutically active compounds in aquatic bodies is a global concern, and suitable treatment technologies are required. In this study, the efficacy of photocatalytic, sonocatalytic, and sonophotocatalytic oxidation processes for the degradation of amoxicillin (AMX) was investigated using visible light with N doped TiO₂ (N-TiO₂) nanoparticles as the catalyst and low-frequency ultrasound in a novel multifrequency reactor. The influence of different operational parameters on the extent of AMX degradation was studied. Sonophotocatalytic oxidation was found more efficient for AMX degradation when compared to photocatalysis or sonocatalysis alone, and may be due to the reduced bandgap of the catalyst, enhanced cavitation effect due to the presence of the solid catalyst, and improved mass transfer of pollutants. AMX degradation during sono, photo, and sonophotocatalytic oxidation processes was in good agreement with pseudo-first-order kinetics. Empirical kinetic models were also developed using multiple linear regression for predicting the degradation efficiency accounting for the operational parameters. Scavenger experiments suggested that ^•OH radicals largely contributed to AMX degradation, and a plausible mechanism for degradation was proposed. Further, possible degradation pathways for all three treatment processes are also proposed after identifying the degradation products.

Optimization of N doping in TiO2 nanotubes for the enhanced solar light mediated photocatalytic H2 production and dye degradation

Herein, we report the optimization of nitrogen (N) doping in TiO₂ nanotubes to achieve the enhanced photocatalytic efficiencies in degradation of dye and H₂ gas evolution under solar light exposure. TiO₂ nanotubes have been produced via hydrothermal process and N doping has been tuned by varying the concentration of urea, being the source for N, by solid-state dispersion process. The structural analysis using XRD showed the characteristic occupancy of N into the structure of TiO₂ and the XPS studies showed the existence of Ti-N-Ti network in the N-doped TiO₂ nanotubes. The obtained TEM images showed the formation of 1D tube-like structure of TiO₂. Diffuse reflectance UV-Vis absorption spectra demonstrated that the N-doped TiO₂ nanotubes can efficiently absorb the photons of UV-Vis light of the solar light. The optimized N-doped TiO₂ nanotubes (TiO₂ nanotubes vs urea @ 1:1 ratio) showed the highest degradation efficiency over methyl orange dye (∼91% in 90 min) and showed the highest rate of H₂ evolution (∼19,848 μmol h^-1.g^-1) under solar light irradiation. Further, the recyclability studies indicated the excellent stability of the photocatalyst for the durable use in both the photocatalytic processes. The observed efficiency was ascribed to the optimized doping of N-atoms into the lattices of TiO₂, which enhanced the optical properties by forming new energy levels of N atoms near the valence band maximum of TiO₂, thereby increased the overall charge separation and recombination resistance in the system. The improved reusability of photocatalyst is attributed to the doping-induced structural stability in N-doped TiO₂. From the observed results, it has been recognized that the established strategy could be promising for synthesizing N-doped TiO₂ nanotubes with favorable structural, optical and photocatalytic properties towards dye degradation and hydrogen production applications.

Preparation and photocatalytic performance of silver-modified and nitrogen-doped TiO2 nanomaterials with oxygen vacancies

A modified hydrothermal method for the synthesis of TiO₂ material to achieve a more efficient visible light response.

Nitrogen-doped TiO2(B) nanobelts enabling enhancement of electronic conductivity and efficiency of lithium-ion storage

To enhance the intrinsic electrical conductivities of TiO₂(B) nanobelts, nitrogen(N)-doped TiO₂(B) nanobelts (N-TNB) were prepared in this study by a facile and cost-effective hydrothermal method using urea as the nitrogen source with TiO₂ (P25) nanoparticles. x-ray photoelectron spectroscopy confirmed that the N-atoms preferentially occupied up to ∼0.516 atom% in the interstitial sites of the N-TNB and the maximum concentration of substituted-N bonds in the N-TNB was ∼0.154 atom%, thereby the total concentration of doped nitrogen elements of ∼0.67 atom% improved the high intrinsic electrical conductivity and ionic diffusivity of the TiO₂(B) nanobelts. The as-prepared N-TNB electrode delivered the highest specific capacity of 133.9 mAh g^-1 in the first cycle, with an exceptional cyclic capacity retention at an ultrafast current rate of 1000 mA g^-1; this is not less than 51% after 500 cycles and represents an excellent rate capability of ∼37 mAh g^-1 at an ultra-high rate of 40 C. These values are among the best ever reported on comparison of the delivered highest discharge capacity of N-TNB at 1000 mA g^-1 and high-rate capabilities of its Li⁺ ion storage with the literature data for N-TNB (∼231.5 mAh g^-1 at a very low current density of 16.75 mA g^-1, ∼0.1 C) of similar materials used in sodium-ion batteries. This implies the potential feasibility of these N-TNB as high-capacity anode materials for next-generation, high-energy-density, electrochemical energy-storage devices.

Enhanced Visible Light Photocatalytic Activity of N and Ag Doped and Co-Doped TiO2 Synthesized by Using an In-Situ Solvothermal Method for Gas Phase Ammonia Removal

Single doping and co-doping of N and Ag on TiO2 were successfully prepared by using an in-situ solvothermal method and their structural properties and chemical compositions were characterized. The results indicated that all photocatalysts displayed in TiO2 anatase crystal phase, and a small mesoporous structure was observed in the doped materials. The main roles of N and Ag on the property and photocatalytic activity of TiO2 were different. The N doping has significantly enhanced homogenous surface morphology and specific surface area of the photocatalyst. While Ag doping was narrowing the band gap energy, extending light absorption toward a visible region by surface plasmon resonance as well as delaying the recombination rate of electron and hole of TiO2. The existence of N in TiO2 lattice was observed in two structural linkages such as substitutional nitrogen (Ti-O-N) and interstitial nitrogen (O-Ti-N). Silver species could be in the form of Ag0 and Ag2O. The photocatalytic performance of the photocatalysts coated on stainless steel mesh was investigated by the degradation of aqueous MB and gas phase NH3 under visible LED light illumination for three recycling runs. The highest photocatalytic activity and recyclability were reached in 5% N/Ag-TiO2 showing the efficiency of 98.82% for methylene blue (MB) dye degradation and 37.5% for NH3 removal in 6 h, which was 2.7 and 4.3 times, respectively. This is greater than that of pure TiO2. This was due to the synergistic effect of N and Ag doping.

The structure and self-regeneration performance of Salix psammophila-activated carbon modified by Ag and N co-doped TiO2

In this study, Salix psammophila activated carbon (AC) was modified by immersing it in an AgNO3 solution and coating it with an N-doped TiO2 film to improve its self-regeneration performance in visible light. Ag+ was adsorbed and reduced to Ag nanoparticles by AC. Ti element only existed as Ti4+, and N element was incorporated into TiO2 mainly in the form of interstitial nitrogen. The photodegradation of Ag-N-TiO2-AC (AC coated with Ag and N co-modified TiO2) was enhanced under visible light irradiation because of its three inherent structures: (1) Ag and N co-modified TiO2 had a smaller average crystal size; (2) with a low bandgap (1.59 eV), the photoresponse region of Ag and N co-modified TiO2 was greatly extended; (3) the lifetime of the photogenerated holes was increased. With the increase in the AgNO3 dosage, the Ag-N-TiO2-AC photodegradation increased, while its adsorption decreased. Because of these synergistic effects, 0.05Ag-0.1N-TiO2-AC (where 0.05 is the dosage of AgNO3, g) presented the best self-regeneration performance under visible light irradiation.

Synthesizing C–N–P-tridoped TiO2 in a Salix psammophila-activated carbon body to enhance its regeneration performance

Loading TiO₂ into an AC body via Salix psammophila pores. C, N, and P atoms were spontaneously doped into TiO₂ lattices. MB removal ratio decreased by 11% after three trials. The synergistic effect of adsorption and photodegradation was enhanced.

High photocatalytic activity of rutile TiO2–BiOBr composites via an in situ synthesis approach

The rutile TiO₂–BiOBr composites had achieved via an in situ synthesis approach, and exhibited the same photocatalytic effect as anatase TiO₂–BiOBr composites.

Recent Advances in Carbonaceous Photocatalysts with Enhanced Photocatalytic Performances: A Mini Review

Photocatalytic processes based on various semiconductors have been widely utilized in different applications, with great potential for use in environmental pollution remediation and sustainable energy generation. However, critical issues, including low light adsorption capability, wide energy bandgap, and unsatisfactory physicochemical stability still seriously limit the practical applications of photocatalysts. As a solution, the introduction of carbonaceous materials with different structures and properties into a photocatalyst system to further increase the activity has attracted much research attention. This mini review surveys the related literatures and highlights recent progress in the development of carbonaceous photocatalysts, which include various metal semiconductors with activated carbon, carbon dots, carbon nanotubes/nanofibers, graphene, fullerene, and carbon sponges/aerogels. Moreover, graphitic carbon nitride is also discussed as a carbon-rich and metal-free photocatalyst. The recently developed synthesis strategies and proposed mechanisms underlying the photocatalytic activity enhancement for different applications are summarized and discussed. Finally, ongoing challenges and the developmental direction for carbonaceous photocatalysts are proposed.

Recent Progress on Titanium Dioxide Nanomaterials for Photocatalytic Applications

Environmental and energy problems have drawn much attention owing to rapid population growth and accelerated economic development. For instance, photocatalysis, "a green technology", plays an important role in solar-energy conversion owing to its potential to solve energy and environmental problems. Recently, many efforts have been devoted to improving visible-light photocatalytic activity by using titanium dioxide as a photocatalyst as a result of its wide range of applications in the energy and environment fields. However, fast charge recombination and an absorption edge in the UV range limit the photocatalytic efficiency of TiO₂ under visible-light irradiation. Many investigations have been undertaken to overcome the limitations of TiO₂ and, therefore, to enhance its photocatalytic activity under visible light. The present literature review focuses on different strategies used to promote the separation efficiency of electron-hole pairs and to shift the absorption edge of TiO₂ to the visible region. Current synthesis techniques used to elaborate several nanostructures of TiO₂ -based materials, recent progress in enhancing visible photocatalytic activity, and different photocatalysis applications will be discussed. On the basis of the studies reported in the literature, we believe that this review will help in the development of new strategies to improve the visible-light photocatalytic performance of TiO₂ -based materials further.

Preparation and photocatalytic activity characterization of activated carbon fiber-BiVO4 composites

Herein, we describe the hydrothermal immobilization of BiVO₄ on activated carbon fibers (ACFs) and characterize the obtained composite by several instrumental techniques, using Reactive Black KN-B (RB5) as a model pollutant for photocatalytic performance evaluation and establishing the experimental conditions yielding maximal photocatalytic activity. The photocatalytic degradation of RB5 is well fitted by a first-order kinetic model, and the good cycling stability and durability of BiVO₄@ACFs highlight the potential applicability of the proposed composite. The enhanced photocatalytic activity of BiVO₄@ACFs compared to those of BiVO₄ and ACFs individually was mechanistically rationalized, and the suggested mechanism was verified by ultraviolet-visible spectroscopy, attenuated total reflectance Fourier-transform infrared spectroscopy, and RB5 degradation experiments. Thus, this work contributes to the development of BiVO₄@ACF composites as effective photocatalysts for environmental remediation applications.

Herein, we describe the hydrothermal immobilization of BiVO₄ on activated carbon fibers, using Reactive Black KN-B photocatalytic performance evaluation and establishing the experimental conditions yielding maximalphotocatalytic activity.

Synergistic Effect of Fluorinated and N Doped TiO₂ Nanoparticles Leading to Different Microstructure and Enhanced Photocatalytic Bacterial Inactivation

This work focuses on the development of a facile and scalable wet milling method followed by heat treatment to prepare fluorinated and/or N-doped TiO₂ nanopowders with improved photocatalytic properties under visible light. The structural and electronic properties of doped particles were investigated by various techniques. The successful doping of TiO₂ was confirmed by X-ray photoelectron spectroscopy (XPS), and the atoms appeared to be mainly located in interstitial positions for N whereas the fluorination is located at the TiO₂ surface. The formation of intragap states was found to be responsible for the band gap narrowing leading to the faster bacterial inactivation dynamics observed for the fluorinated and N doped TiO₂ particles compared to N-doped TiO₂. This was attributed to a synergistic effect. The results presented in this study confirmed the suitability of the preparation approach for the large-scale production of cost-efficient doped TiO₂ for effective bacterial inactivation.

Preparation of highly mesoporous honeycomb-like TiO2 and its excellent application

In this work, titanium sulfate and hydrazine hydrate were used as raw materials to fabricate highly mesoporous honeycomb TiO₂via a two-step hydrothermal and calcination method.

Enhanced efficiency of over 10% in dye-sensitized solar cells through C and N single- and co-doped TiO2 single-layer electrodes

An efficiency of 10.2% is achieved using substitutional C and interstitial N atoms for C and N single- and co-doped TiO₂ DSCs.

Facile preparation of yolk–shell structured Si/SiC@C@TiO2 nanocomposites as highly efficient photocatalysts for degrading organic dye in wastewater

The prepared yolk–shell Si/SiC@C@TiO₂ nanospheres show a strong photon absorbance throughout the visible light region, and excellent photocatalytic performance for degrading methyl blue in water under UV and visible light irradiation.

Nitrogen-doped titanium dioxide (N-doped TiO2) for visible light photocatalysis

Energy level diagrams for undoped and N-doped TiO₂ for visible light induced photocatalytic application.

Hierarchical rattle-like N-doped anatase TiO2 superstructure: one-pot synthesis, morphological evolution and superior visible light photocatalytic activity

A novel N-doped rattle-like hierarchical anatase superstructure with a spherical porous core and hierarchical shell composed of ultrathin nanosheets was synthesized via a facile template-free method, which exhibits enhanced photocatalytic activity under visible light illumination.

Improved light absorption and photocatalytic activity of Zn,N-TiO2−x rich in oxygen vacancies synthesized by nitridation and hydrogenation

Compared with N-TiO₂ and Zn,N-TiO₂ samples, Zn,N-TiO_2−x rich in oxygen vacancies demonstrates high photocatalytic activity.

Fabrication of TiO2/porous carbon nanofibers with superior visible photocatalytic activity

TiO₂/PCNFs heterostructures were successfully fabricated by combining an electrospinning technique with a hydrothermal method, exhibiting enhanced visible photocatalytic activity.