Microwave-Assisted Synthesis of Carbon-Based (N, Fe)-Codoped TiO2 for the Photocatalytic Degradation of Formaldehyde

Synthesis of efficient light harvesting Cr, N Co-doped TiO2 nanoparticles for enhanced visible light photocatalytic degradation of xanthene dyes; eosin yellow and rose bengal

To solve the problem of water pollution, using environment friendly and cost effective method in short time is the need of hour. In this work, chromium (Cr) and nitrogen (N) co-doped TiO2 nanoparticles were synthesized and were used for the photocatalytic degradation of dyes under visible light. The synergistic effect of metal and non-metal co-dopants added would result in appropriate reduction of band gap {from 3.2 eV of TiO2 to 2.67 eV}, decrease in recombination rate of charge carriers by trapping electrons and holes, and in better light harvesting capacity. Nanoparticles were synthesized by sol-gel method and characterized using ultraviolet-visible (UV-VIS) spectroscopy, fourier transform infrared (FTIR) spectroscopy, atomic force microscopy (AFM), zeta potential, X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) analysis, field emission scanning electron microscopy (FE-SEM), and RAMAN spectroscopy. Eosin yellow (EY) and rose bengal (RB) were subjected to photocatalytic degradation under solar light to check the photocatalytic activity of the synthesized nanoparticles. Effects of dye concentration, the concentration of nanoparticles, time, and pH were investigated to optimize the parameters. The results obtained were remarkable for 20 ppm EY solution took 10 min using 1 gL-1 NPs at pH 3 and 10 ppm RB solution took 5 min using 0.75 gL-1 NPs at pH 5.78 (original pH) for complete degradation. Kinetics studies were also performed and both dyes followed pseudo-second-order kinetics with R2 values 0.99312 and 0.99712 for EY and RB, respectively. The study of degraded products was conducted using high-performance liquid chromatography (HPLC) hyphenated with electron spray ionization mass spectroscopy (ESI-MS) (LC-MS) and possible degradation pathways were made for both dyes. A reusability test was also performed showing the efficiency of the particles was up to 88% after 3 cycles of use. These notable results can be attributed to the efficient removal of organic pollutants using the proposed dopants in this study.

Synthesis and Characterization of Fe Doped Aurivillius-Phase PbBi2Nb2O9 Perovskite and Their Photocatalytic Activity on the Degradation of Methylene Blue

A simple solid-state reaction was applied to synthesize Fe-doped perovskite-type PBFNO catalysts, and methylene blue decomposition studies were performed in the form of visible light according to the changes in the Fe doping content (0.4 to 1.9 mol ratio compared with Bi mol) and the amount of catalyst used (0.05 to 0.2 g used). As the Fe doping content increases, the absorbance and bang gap energy of the PBFNOs sample rapidly increase and decrease, respectively, because the Fe dopant in the PBNO lattice acts as an intermediate band between the valence and conduction bands of the PBNO and reduces the band gap energy. As a result, it showed a performance degradation of approximately 42% compared to the maximum performance. In addition, the presence of Fe dopants in the PBNO lattice greatly reduces the intensity of the photoluminescent lines. This is because the Fe dopant can play an important role in light-induced electron transfer and as a hole trap, reducing the recombination rate. Additionally, when too much photocatalyst was used (>0.1 g used), the Fe dopant played an important role as a light-induced electron transfer and hole trap, reducing the recombination rate and lowering the overall photocatalytic activity by 51%. In particular, 0.1 g of PBNO-0.2-F showed continuous catalytic activity, even when the photocatalytic reaction proceeded for 180 min. Therefore, this study demonstrates that the Fe-doped aurivillius-phase PBFNO photocatalyst is very promising for the dye manufacturing industry.

Enhanced Fe-TiO2 Solar Photocatalysts on Porous Platforms for Water Purification

In this study, polyethylene glycol-modified titanium dioxide (PEG-modified TiO2) nanopowders were prepared using a fast solvothermal method under microwave irradiation, and without any further calcination processes. These nanopowders were further impregnated on porous polymeric platforms by drop-casting. The effect of adding iron with different molar ratios (1, 2, and 5%) of iron precursor was investigated. The characterization of the produced materials was carried out by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. Optical characterization of all the materials was also carried out. SEM showed that pure TiO2 and Fe-TiO2 nanostructures presented similar nanosized and spherical particles, which uniformly covered the substrates. From XRD, pure TiO2 anatase was obtained for all nanopowders produced, which was further confirmed by Raman spectroscopy on the impregnated substrates. XPS and UV-VIS absorption spectroscopy emission spectra revealed that the presence of Fe ions on the Fe-TiO2 nanostructures led to the introduction of new intermediate energy levels, as well as defects that contributed to an enhancement in the photocatalytic performance. The photocatalytic results under solar radiation demonstrated increased photocatalytic activity in the presence of the 5% Fe-TiO2 nanostructures (Rhodamine B degradation of 85% after 3.5 h, compared to 74% with pure TiO2 for the same exposure time). The photodegradation rate of RhB dye with the Fe-TiO2 substrate was 1.5-times faster than pure TiO2. Reusability tests were also performed. The approach developed in this work originated novel functionalized photocatalytic platforms, which were revealed to be promising for the removal of organic dyes from wastewater.

Enhancement of sonocatalytic degradation of organic dye by using titanium dioxide (TiO2)/activated carbon (AC) derived from oil palm empty fruit bunch

A novel titanium dioxide/activated carbon (TiO₂/AC) composite where AC derived from oil palm empty fruit bunch (EFB) was synthesised by using sol-gel method. All the samples were characterised by using X-ray diffraction (XRD), scanning electron microscopy-energy dispersive X-ray (SEM-EDX), Fourier transformed infrared (FTIR), thermogravimetric analysis (TGA) and surface analyser. SEM analysis showed that TiO₂ particles were successfully embedded and well distributed on the AC surface. The elemental composition analysis found that the TiO₂/AC composite contained titanium (Ti), oxygen (O) and carbon (C) atoms. Meanwhile, the appearance of new band at about 960 cm^-1 which assigned to the Ti-O stretching was observed in the FTIR spectra when the AC was incorporated into TiO₂. TGA analysis showed that the weight loss of 32 wt.% from 150 to 550 °C was due to the decomposition of amorphous carbon layers and loss of hydroxyl groups on TiO₂. It was found that the TiO₂/AC composite had better performance in the sonocatalytic degradation of malachite green as compared to the individual AC and TiO₂ because the TiO₂/AC composite had dual functionality and huge number of active sites which could promote the mass transfer of dye molecules towards catalyst surface. By using 1.5 g/L of TiO₂/AC composite which calcined at 700 °C on 100 mL of 200 mg/L of malachite green at solution pH of 7, a degradation efficiency of 87.11% had been achieved after 30 min of ultrasonic irradiation. A lower chemical oxygen demand (COD) removal (81.75%) was observed because the structured dye molecules underwent mineralisation process during the sonocatalytic degradation to generate intermediate compounds. The TiO₂/AC composite was able to be recycled and still achieved a high degradation efficiency of 76.78% after second catalytic cycle as compared to the fresh TiO₂/AC composite with degradation efficiency of 87.11%. In conclusion, the TiO₂/AC composite had high reusability and promising for practical applications in textile industry.

Fe/Ni Bimetallic Organic Framework Deposited on TiO2 Nanotube Array for Enhancing Higher and Stable Photoelectrochemical Activity of Oxygen Evaluation Reaction

Photoelectrochemical (PEC) water splitting is a promising strategy to improve the efficiency of oxygen evolution reactions (OERs). However, the efficient adsorption of visible light as well as long-term stability of light-harvesting electrocatalysis is the crucial issue in PEC cells. Metal–organic framework (MOF)-derived bimetallic electrocatalysis with its superior performance has wide application prospects in OER and PEC applications. Herein, we have fabricated a nickel and iron bimetallic organic framework (FeNi-MOF) deposited on top of anodized TiO₂ nanotube arrays (TNTA) for PEC and OER applications. The FeNi-MOF/TNTA was incorporated through the electrochemical deposition of Ni²⁺ and Fe³⁺ onto the surface of TNTA and then connected with organic ligands by the hydrothermal transformation. Therefore, FeNi-MOF/TNTA demonstrates abundant photoelectrocatalytic active sites that can enhance the photocurrent up to 1.91 mA/cm² under 100 mW/cm² and a negligible loss in activity after 180 min of photoreaction. The FeNi-MOF-doped photoanode shows predominant photoelectrochemical performance due to the boosted excellent light-harvesting ability, rapid photoresponse, and stimulated interfacial energy of charge separation under the UV-visible light irradiation conditions. The results of this study give deep insight into MOF-derived bimetallic nanomaterial synthesis for photoelectrochemical OER and provide guidance on future electrocatalysis design.

Constructing a Z-scheme Heterojunction of Egg-Like Core@shell CdS@TiO₂ Photocatalyst via a Facile Reflux Method for Enhanced Photocatalytic Performance

A well designed and accurate method of control of different shell thickness and electronic transmission in a Z-scheme core@shell system is conducive to obtaining an optimum photocatalytic performance. Herein, the Z-scheme heterojunction of egg-like core@shell CdS@TiO₂photocatalysts with controlled shell thickness (13 nm, 15 nm, 17 nm, 22 nm) were synthesized by a facile reflux method, and the CdS@TiO₂ structure was proved by a series of characterizations. The photodegradation ratio on methylene blue and tetracycline hydrochloride over the 0.10CdS@TiO₂ composites with TiO₂ shell thickness of 17 nm reached 90% in 250 min and 91% in 5 min, respectively, which was almost 9.8 times and 2.6 times than that of TiO₂ and CdS on rhodamine B respectively under visible light. Besides, the higher total organic carbon removal ratio indicated that most of the pollutants were degraded to CO₂ and H₂O. The Z-scheme electronic transfer pathway was studied through radical species trapping experiments and electron spin resonance spectroscopy. Moreover, the relationship between shell thickness and photocatalytic activity demonstrated that different shell thickness affects the separation of the electron and holes, and therefore affected the photocatalytic performance. In addition, the effects of pollutants concentration, pH, and inorganic anions on photocatalytic performance were also investigated. This work can provide a novel idea for a well designed Z-scheme heterojunction of core@shell photocatalysts, and the study of photocatalytic performance under different factors has guiding significance for the treatment of actual wastewater.

Distinguishing between Deep Trapping Transients of Electrons and Holes in TiO2 Nanotube Arrays Using Planar Microwave Resonator Sensor

A large signal direct current (DC) bias and a small signal microwave bias were simultaneously applied to TiO₂ nanotube membranes mounted on a planar microwave resonator. The DC bias modulated the electron concentration in the TiO₂ nanotubes and was varied between 0 and 120 V in this study. Transients immediately following the application and removal of DC bias were measured by monitoring the S-parameters of the resonator as a function of time. The DC bias stimulated Poole-Frenkel-type trap-mediated electrical injection of excess carriers into TiO₂ nanotubes, which resulted in a near-constant resonant frequency but a pronounced decrease in the microwave amplitude due to free electron absorption. When ultraviolet illumination and DC bias were both present and then stepwise removed, the resonant frequency shifted due to trapping-mediated change in the dielectric constant of the nanotube membranes. Characteristic lifetimes of 60-80, 300-800, and ∼3000 s were present regardless of whether light or bias was applied and were also observed in the presence of a hole scavenger, which we attributed to oxygen adsorption and deep electron traps, whereas another characteristic lifetime >8000 s was only present when illumination was applied, and is attributed to the presence of hole traps.

Sol-Gel Hydrothermal Synthesis and Visible Light Photocatalytic Degradation Performance of Fe/N Codoped TiO₂ Catalysts

Using Ti(OC₄H₉)₄ as a precursor, Fe(NO₃)₃⋅9H₂O as the source of iron, and NH₄NO₃ as the source of nitrogen, an Fe/N codoped TiO₂ catalyst was prepared using a sol-gel hydrothermal method. The as-prepared powders were characterized using X-ray powder diffraction, electron spectroscopy for chemical analysis, Fourier-transform infrared spectroscopy, and ultraviolet-visible spectrophotometry. Fe and N codoping resulted in decreased crystallite size and increased specific surface area. Results of the photocatalytic degradation of acid orange 7 (AO7) in a continuous-flow fluidized-bed reactor indicated that the maximum decolorization (more than 90%) of AO7 occurred with the Fe/N-TiO₂ catalyst (dosage of 20 g/L) when a combination of visible light irradiation for 10 h HRT (hydraulic retention time), and a heterogeneous system was used. The AO7 degradation efficiency was considerably improved by increasing the hydraulic retention time from 2.5 to 10 h or by reducing the initial AO7 concentration from 300 to 100 mg/L. The reaction rate increased with the light intensity and the maximum value occurred at 35 mW/cm²; moreover, the efficiency of the AO7 degradation increased when the pH decreased with maximum efficiency at pH 3.

The Photocatalytic Application of Semiconductor Stibnite Nanostructure Synthesized via a Simple Microwave-Assisted Approach in Propylene Glycol for Degradation of Dye Pollutants and its Optical Property

Stibnite (Sb₂S₃) semiconducting material was successfully synthesized by a rapid and facile microwave route using antimony chloride (SbCl₃) and sodiumthiosulfate (Na₂S₂O₃) dissolved in propylene glycol (PG) containing different hydroxyethyl cellulose (HEC) masses. The phase identification, morphology, and elemental composition of products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), field- emission scanning electron microscopy (FE-SEM), energy dispersive X-ray (EDX) spectroscopy, and Fourier transform infrared spectroscopy (FTIR). The results revealed the orthorhombic phase of Sb₂S₃ single crystal-forming sheaf-like nanostructure, and a possible formation mechanism was proposed and discussed. Its direct band gap calculated from UV-visible absorption is 1.60 eV. In this research, the photocatalytic activities of Sb₂S₃ nanostructure were investigated through the degradation of methyl orange (MO) and methylene blue (MB) under visible light irradiation. The as-obtained 0.30 g HEC-added solution (0.3 HEC-Sb₂S₃) photocatalyst exhibited better photocatalytic activity than the other products, which degraded 91% of MO within 300 min and 90% of MB within 240 min under the Xe-lamp irradiation. The first-order plot was fitted with this experiment which the rate constant (k) of 0.3 HEC-Sb₂S₃ for MO and MB degradation are 0.0085 and 0.0098 min^-1, respectively. Therefore, the new experience with a novel and simple synthetic procedure of Sb₂S₃ photocatalyst that exhibits the characteristics of a highly effective photocatalyst under visible light irradiation was discovered.

Highly efficient Zr doped-TiO2/glass fiber photocatalyst and its performance in formaldehyde removal under visible light

Zr-doped-TiO₂ loaded glass fiber (ZT/GF) composite photocatalysts with different Zr/Ti ratios were prepared with a sol-gel process. Zr⁴⁺ can replace Ti⁴⁺ in the TiO₂ lattice, which is conducive to forming the anatase phase and reducing the calcination temperature. The glass fiber carrier was responsible for better dispersion and loading of Zr-doped-TiO₂ particles, improving the applicability of the Zr-doped-TiO₂. The ZT/GF photocatalysts were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FT-IR), ultraviolet-visible spectroscopy (UV-vis) and Barrett-Joyner-Halenda (BJH). The performance of photocatalysts with different loading was evaluated in formaldehyde degradation under visible light at room temperature. ZT/GF0.2 exhibited the highest activity, with a formaldehyde removal rate as high as 95.14% being observed, which is better than that of the photocatalyst particles alone. The stability of the catalyst was also tested, and ZT/GF exhibited excellent catalytic performance with 94.38% removal efficiency, even after seven uses.

Photocatalytic degradation of formaldehyde by PAN nonwoven supported Fe(iii) catalysts under visible light irradiation

Amidoximated PAN nonwoven fabrics coordinated with Fe(iii) as a photocatalyst for formaldehyde degradation by activating O₂ under visible irradiation.

Photodegradation performance and recyclability of a porous nitrogen and carbon co-doped TiO2/activated carbon composite prepared by an extremely fast one-step microwave method

Porous (C,N)-TiO₂/AC) composite bulk was prepared by a fast one-step microwave irradiation. It has very good photocatalytic properties and recyclability.