Triboelectric Nanogenerators for Self-Powered Degradation of Chemical Pollutants

Environmental and human health is severely threatened by wastewater and air pollution, which contain a broad spectrum of organic and inorganic pollutants. Organic contaminants include dyes, volatile organic compounds (VOCs), medical waste, antibiotics, pesticides, and chemical warfare agents. Inorganic gases such as CO2, SO2, and NO x are commonly found in polluted water and air. Traditional methods for pollutant removal, such as oxidation, physicochemical techniques, biotreatment, and enzymatic decomposition, often prove to be inefficient, costly, or energy-intensive. Contemporary solutions like nanofiber-based filters, activated carbon, and plant biomass also face challenges such as generating secondary contaminants and being time-consuming. In this context, triboelectric nanogenerators (TENGs) are emerging as promising alternatives. These devices harvest ambient mechanical energy and convert it to electrical energy, enabling the self-powered degradation of chemical pollutants. This Review summarizes recent progress and challenges in using TENGs as self-powered electrochemical systems (SPECs) for pollutant degradation via photocatalysis or electrocatalysis. The working principles of TENGs are discussed, focusing on their structural flexibility, operational modes, and ability to capture energy from low-frequency mechanical stimuli. The Review concludes with perspectives and suggestions for future research in this field, hoping to inspire further interest and innovation in developing TENG-based SPECs, which represent sustainable and eco-friendly solutions for pollutant treatment.

Graphitic carbon nitride (g-C3N4)-assisted materials for the detection and remediation of hazardous gases and VOCs

Graphitic carbon nitride (g-C3N4)-based materials are attracting attention for their unique properties, such as low-cost, chemical stability, facile synthesis, adjustable electronic structure, and optical properties. These facilitate the use of g-C3N4 to design better photocatalytic and sensing materials. Environmental pollution by hazardous gases and volatile organic compounds (VOCs) can be monitored and controlled using eco-friendly g-C3N4- photocatalysts. Firstly, this review introduces the structure, optical and electronic properties of C3N4 and C3N4 assisted materials, followed by various synthesis strategies. In continuation, binary and ternary nanocomposites of C3N4 with metal oxides, sulfides, noble metals, and graphene are elaborated. g-C3N4/metal oxide composites exhibited better charge separation that leads to enhancement in photocatalytic properties. g-C3N4/noble metal composites possess higher photocatalytic activities due to the surface plasmon effects of metals. Ternary composites by the presence of dual heterojunctions improve properties of g-C3N4 for enhanced photocatalytic application. In the later part, we have summarised the application of g-C3N4 and its assisted materials for sensing toxic gases and VOCs and decontaminating NOx and VOCs by photocatalysis. Composites of g-C3N4 with metal and metal oxide give comparatively better results. This review is expected to bring a new sketch for developing g-C3N4-based photocatalysts and sensors with practical applications.

A Novel Application of Photocatalysis: A UV-LED Photocatalytic Device for Controlling Diurnal Evaporative Fuel Vapor Emissions from Automobiles

A novel application of photocatalysis was investigated to reduce diurnal evaporative fuel vapor emissions from automobiles. A light-weight annulus photocatalytic device was designed, fabricated, and characterized for its performance for the oxidation of diurnal evaporative fuel vapor emissions. The prototype photocatalytic device was made with PVC pipe and ultraviolet (λ = 365 nm) light emitting diodes (UV LEDs) as light sources. Commercially available Evonik P25 TiO2 was used as the photocatalyst. The study results demonstrate that the UV LED photocatalytic device is capable of reducing diurnal evaporative fuel vapor emissions from automobiles by 60 wt%. However, the presence of high concentrations of light alkanes and aromatic fuel vapors in the diurnal emissions may limit the longevity of the device due to photocatalyst deactivation. Further development of the idea to enhance the longevity of its performance is recommended.

Synthesis and Photocatalytic Activity for Toluene Removal of CDs/TiO2 - Zeolite Y

Hydrothermally synthesized carbon nanodots (CDs) were impregnated on TiO2. The product (CDs/TiO2) was mechanically mixed with zeolite Y for application in toluene photocatalytic oxidation reaction under UV radiation. Material properties of the samples were investigated by different methods. Toluene vapor was chosen as a typical volatile organic compound to investigate the performance of CDs/TiO2 – zeolite Y photocatalyst when these technological parameters were changed: toluene concentration, gas flow rate, humidity and UV light intensity. In each reaction, only one parameter was changed and the remaining conditions were fixed. The toluene concentrations at the beginning and the end of each reaction were analyzed with the use of gas chromatography (GC). The results of different reaction conditions show the trends for toluene treatment of the CDs/TiO2 – zeolite Y catalyst, thereby providing specific explanations for these trends. The experiments also show that toluene removal is highest when the toluene concentration in the inlet gas is 314 ppmv, the flow rate is 3 L/h, the humidity is 60%, and the catalyst (CDs/TiO2 – zeolite Y composite with 70% zeolite in weight) is illuminated by 4 UV lamps. Copyright © 2022 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0). 

Photocatalytic VOCs Degradation Efficiency of Polypropylene Membranes by Incorporation of TiO2 Nanoparticles

A class of serious environmental contaminants related to air, namely volatile organic compounds (VOCs), has currently attracted global attention. The present study aims to remove harmful VOCs using as-prepared polypropylene membrane + TiO₂ nanoparticles (PPM + TiO₂ NPs) via the photocatalytic gas bag A method under UV light irradiation. Here, formaldehyde was used as the target VOC. The PPM + TiO₂ NPs material was systematically characterized using various microscopic and spectroscopic techniques, including field emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, Fourier-transform infrared spectroscopy, ultraviolet-visible diffuse reflectance spectroscopy, photoluminescence spectroscopy, and contact angle measurements. These results confirm the successful preparation of PPM + TiO₂ NPs, which can be applied to the degradation of VOCs. Photocatalytic degradation of formaldehyde gas reached 70% within 1 h of UV illumination. The energy bandgap and photoluminescence intensity reductions are responsible for the improved photocatalytic activity. These characteristics increase the charge transport while decreasing the recombination of electron-hole pairs.

Suppression of Airway Allergic Reactions by a Photocatalytic Filter Using Mouse Model

Photocatalytic filters installed in air purifiers have been used to purify spaces by decomposing allergenic substances. However, we have not found any reports that evaluate the effectiveness of photocatalytic filters in suppressing allergic reactions in living organisms. In this study, we intratracheally instilled ovalbumin (OVA) into OVA-sensitized mice after the OVA was photocatalyzed by a titanium dioxide (TiO₂) filter, and verified the experimental model for evaluating the allergy-suppressing effect of photocatalysts. Mice were sensitized to OVA (10 µg/mouse) four times, and were intratracheally instilled with OVA (10 µg/mouse) after photocatalysis three times. Non-sensitized animals were instilled with normal saline following the same exposure schedule. The mice were dissected 24 h after final exposure. The OVA after photocatalysis significantly decreased the number of eosinophils in bronchoalveolar lavage fluid, and the concentration of OVA-specific IgE and IgG1 in serum, which were elevated in untreated OVA. Moreover, our experimental model showed the suppression of allergic reactions in mice, along with the decomposition of OVA after photocatalysis using the photocatalytic filter. Taken together, our experimental model for evaluating allergic reactions in the respiratory tract suggested that the allergy-suppressing effect of the photocatalytic filter can be evaluated.

Ultraviolet photocatalytic oxidation technology for indoor volatile organic compound removal: A critical review with particular focus on byproduct formation and modeling

Photocatalytic oxidation (PCO)-based air filters are gaining attention owing to their capacity for indoor pollutant removal. This review summarized the application of ultraviolet-photocatalytic oxidation (UV-PCO) in heating, ventilation, and air conditioning (HVAC) systems, including the modeling studies, reactor designs, the influence of operational conditions, with emphasis on the common issue of byproduct generation, and the resulting indoor byproduct exposure levels. As a result, the concentrations of the typical byproducts for the most challenging pollutants were relatively low, except for the PCO of ethanol. Hence, UV-PCO is not recommended for buildings with high ethanol concentrations. Based on the formation of the formaldehyde, a new exposure-based evaluation standard for UV-PCO was developed to evaluate the feasibility of integrating UV-PCO reactors into an HVAC system. Then, applying the newly developed evaluation standard on a developed database (data size: 174) from the literature, 32.5% of the cases were identified as suitable for HVAC system applications in residential and commercial buildings, and all cases could be used for industrial buildings. Finally, a case study was conducted to develop a support vector machine (SVM) classification model with good accuracy, and challenging compound types, inlet concentrations, and air velocity were found to be the main parameters affecting the applicability of UV-PCO.

An Insight into Geometries and Catalytic Applications of CeO2 from a DFT Outlook

Rare earth metal oxides (REMOs) have gained considerable attention in recent years owing to their distinctive properties and potential applications in electronic devices and catalysts. Particularly, cerium dioxide (CeO2), also known as ceria, has emerged as an interesting material in a wide variety of industrial, technological, and medical applications. Ceria can be synthesized with various morphologies, including rods, cubes, wires, tubes, and spheres. This comprehensive review offers valuable perceptions into the crystal structure, fundamental properties, and reaction mechanisms that govern the well-established surface-assisted reactions over ceria. The activity, selectivity, and stability of ceria, either as a stand-alone catalyst or as supports for other metals, are frequently ascribed to its strong interactions with the adsorbates and its facile redox cycle. Doping of ceria with transition metals is a common strategy to modify the characteristics and to fine-tune its reactive properties. DFT-derived chemical mechanisms are surveyed and presented in light of pertinent experimental findings. Finally, the effect of surface termination on catalysis by ceria is also highlighted.

Quantification of volatile organic compounds by secondary electrospray ionization-high resolution mass spectrometry

Secondary electrospray ionization coupled with high resolution mass spectrometry (SESI-HRMS) is a direct mass spectrometry technique, which can identify trace volatile organic compounds (VOCs) in real time without sample pretreatment and chromatographic separation. SESI-HRMS has been successfully applied in multiple applications, including breath analysis, animals and plants VOCs emissions, analysis of headspace of cell cultures and indoor and outdoor air. The range of areas where the technique can potentially have a substantial impact is very broad. However, one critical aspect that requires further development to consolidate the technique is absolute quantification. Therefore, in this study we aim to develop a quantitative method for eight representative VOCs, including ketones (acetone, 2-butanone and 2-pentanone), alkenes (isoprene and α-terpinene) and aromatics (toluene, styrene and mesitylene). The mass spectrometric platform includes a commercial SESI source hyphenated with a Q-Exactive hybrid quadrupole Orbitrap high resolution mass spectrometer. Within the concentration range of 0-100 ppbv studied, the optimal coefficient of determination for linear regression (R² = 0.993-0.999) between signal intensity and concentration is obtained in the range of 0-10 ppbv for all eight VOCs. The detection limits range between 3 (2-Pentanone) and 15 (Acetone) pptv. The intra-day (n = 10) and inter-day (n = 30) coefficients of variation (CV) are ≤ 6% and ≤10%, respectively. Finally the method is applied for the fast evaluation (<5 min) of different materials widely used for the collection, storage or pretreatment of gas sample. Better recovery of trace levels of eight VOCs is observed for PTFE gas sampling bag as compared to Nalophan and Tedlar bags; when Nafion tube is used to pretreat the gas sample, recovery of ≤50% are obtained for 2-pentanone, α-terpinene and all three aromatics.

Synergistic effect of adsorption and photocatalysis for the degradation of toluene by TiO2 loaded on ACF modified by Zn(CH3COO)2

Activated carbon fiber (ACF) was modified by Zn(NO₃)₂, ZnCl₂, and Zn(CH₃COO)₂), respectively, and then, TiO₂ was loaded on the modified ACFs. The adsorption and photocatalysis performance were explored through the removal of toluene, and TiO₂/ACF-_Ac modified by Zn(CH₃COO)₂) with the best toluene degradation performance was selected. The characterization results of a scanning electron microscope (SEM), X-ray diffraction spectra (XRD), and Fourier transform infrared spectrometer (FTIR) indicated that the samples were rough, and TiO₂ was mainly loaded on the surface containing large amount of oxygen-containing functional groups in anatase phase. An ultraviolet-visible diffuse reflectance spectrophotometer (UV-vis DRS) revealed that the catalyst enhanced the light response range. The photoelectric chemical experiment results demonstrated that the modified ACFs remarkably improved the charge transmission and the separation efficiency of electrons and holes. The adsorption saturation time reached 40 h and toluene photodegradation rate was 70%. Four toluene degradation intermediate products were determined by GC-MS, and the removal mechanism of toluene by TiO₂/ACF-_Ac was discussed.

Photocatalytic oxidation of nitrogen oxides (NOx) using Ag- and Pt-doped TiO2 nanoparticles under visible light irradiation

In this work, titanium dioxide nanoparticles (TiO₂ NPs) and modified TiO₂ NPs with silver (Ag) or platinum (Pt) dopant were developed through photodeposition method for the NO_x conversion into nitric acid (HNO₃) under visible light irradiation. The formed photocatalysts TiO₂, Ag/TiO₂, and Pt/TiO₂ nanocomposites were characterized by utilizing TEM, SEM, energy-dispersive X-ray analysis (EDX), XRD, UV/visible diffuse reflectance spectroscopy (UV-Vis DRS), and FT-IR. It had been investigated that an enhancement within the conversion of NO_x into HNO₃ was increased from 34.3 to 78.3% for Ag/TiO₂ and from 35.2 to 78.5% for Pt/TiO₂ under visible light irradiation conditions at room temperature for less than 2 h. The photodegradation rate order of NO_x under visible light irradiation is Pt/TiO₂ ~ Ag/TiO₂ > TiO₂. A possible mechanism for the catalytic conversion of NO_x gases has been proposed, which depends on the photogeneration of electrons and holes after the excitation of nanocatalysts under visible radiation that promoted superoxide and hydroxyl ions, which can depredate NO_x gases. This approach of NO_x photocatalytic conversion is characterized by its chemical stability, low cost, high efficiency, simple operation, and strong durability than traditional methods.

Visible Light Photodegradation of Formaldehyde over TiO2 Nanotubes Synthesized via Electrochemical Anodization of Titanium Foil

In this study, a series of TiO₂ nanotubes (NTs) were synthesized employing electrochemical anodization of titanium foil in an ionic liquid solution containing a mixture of glycerol and choline chloride, acting as electrolyte. The as-synthesized TiO₂ NTs were calcined at 350, 450, or 550 °C for a 2 h duration to investigate the influence of calcination temperature on NTs formation, morphology, surface properties, crystallinity, and subsequent photocatalytic activity for visible light photodegradation of gaseous formaldehyde (HCHO). Results showed that the calcination temperature has a significant effect on the structure and coverage of TiO₂ NTs on the surface. Freshly synthesized TiO₂ NTs showed better-ordered structure compared to calcined samples. There was significant pore rupture with increasing calcination temperature. The transformation from anatase to rutile phase appeared after calcination at 450 °C and the weight fraction of the rutile phase increased from 19% to 36% upon increasing the calcination temperature to 550 °C. The band gaps of the TiO₂ NTs were in the range from 2.80 to 2.74 eV, shifting the active region of the materials to visible light. The presence of mixed anatase–rutile TiO₂ phases in the sample calcined at 450 °C showed enhanced photoactivity, which was confirmed by the 21.56 mg∙L⁻¹∙g⁻¹ removal of gaseous formaldehyde under 120 min of visible light irradiation and displayed enhanced quantum yield, ∅_HCHO of 17%.

Photochemical degradation of toluene in gas-phase under UV/visible light graphene oxide-TiO2 nanocomposite: influential operating factors, optimization, and modeling

The current study aimed to investigate the removal efficiency of toluene using synthesized titanium dioxide-graphene oxide composites under visible light and UV irradiation. The characterization of synthesized composites was examined by field emission scanning electron microscope equipped with energy dispersive, X-ray diffraction and fourier transforms infrared. In order to find the optimum of the main experimental parameters affecting the removal efficiency of toluene including the length of the reactor, initial concentration, and flow rates, central composite design together with response surface methodology with R software was used. The initial concentration of toluene in the inlet of the reactor as well as its concentration in the outlet was measured using gas chromatography with the flame ionization detector. Analysis of variance results for the quadratic model showed that the highly significant and simple linear regression was established as a predicting model. Multiple and adjusted R² were 0.965 and 0.974 for UV irradiation GO-TiO₂ model and 0.951 and 0.959 for visible light GO-TiO₂ model, respectively. As such, the differences less than 0.2 between multiple and adjusted R² in two models indicate that two examined models were fitted well. The highest removal efficiency of toluene using UV irradiation GO-TiO₂ and visible light GO-TiO₂ was obtained at optimum condition; length of reactor 40 cm, initial concentration of 0.1 ppm, and flow rate equal to 1 l min^-1, with 97.7 and 77.2%, respectively. The results indicated that the removal efficiency of toluene increased considerably with rising the length of the reactor, decreasing flow rates, and initial concentration.

Physicochemical characteristics and photocatalytic performance of TiO2/SiO2 catalyst synthesized using biogenic silica from bamboo leaves

In this work, TiO₂/SiO₂ composite photocatalysts were prepared using biogenic silica extracted from bamboo leaves and titanium tetraisopropoxide as a titania precursor via a sol–gel mechanism. A study of the physicochemical properties of materials as a function of their titanium dioxide content was conducted using Fourier transform infrared spectroscopy, a scanning electron microscope, a diffuse reflectance ultraviolet-visible (UV-vis) spectrophotometer, and a gas sorption analyzer. The relationship between physicochemical parameters and photocatalytic performance was evaluated using the methylene blue (MB) photocatalytic degradation process under UV irradiation with and without the addition of H₂O₂ as an oxidant. The results demonstrated that increasing the TiO₂ helps enhance the parameters of specific surface area, the pore volume, and the particle size of titanium dioxide, while the band gap energy reaches a maximum of 3.21 eV for 40% and 60% Ti content. The composites exhibit photocatalytic activity with the MB degradation with increasing photocatalytic efficiency since the composites with 40 and 60% wt. of TiO₂ demonstrated the higher degradation rate compared with TiO₂ in the presence and absence of H₂O₂. This higher rate is correlated with the higher specific surface area and band gap energy compared with those of TiO₂.

Recent Advances and Applications of Semiconductor Photocatalytic Technology

Along with the development of industry and the improvement of people’s living standards, peoples’ demand on resources has greatly increased, causing energy crises and environmental pollution. In recent years, photocatalytic technology has shown great potential as a low-cost, environmentally-friendly, and sustainable technology, and it has become a hot research topic. However, current photocatalytic technology cannot meet industrial requirements. The biggest challenge in the industrialization of photocatalyst technology is the development of an ideal photocatalyst, which should possess four features, including a high photocatalytic efficiency, a large specific surface area, a full utilization of sunlight, and recyclability. In this review, starting from the photocatalytic reaction mechanism and the preparation of the photocatalyst, we review the classification of current photocatalysts and the methods for improving photocatalytic performance; we also further discuss the potential industrial usage of photocatalytic technology. This review also aims to provide basic and comprehensive information on the industrialization of photocatalysis technology.

Effective photoreduction of graphene oxide for photodegradation of volatile organic compounds

Nowadays, humans spend most of their time indoors and are frequently exposed to volatile organic compounds (VOCs) from various sources. The photocatalytic oxidation (PCO) method is a relatively more efficient method than the adsorption method for removing VOCs from the environment. In this work, graphene oxide (GO) was partially reduced via photoreduction under ultraviolet light (UV-A) irradiation and then used as a photocatalyst to degrade VOCs. After photoreduction, the band gap of the partially reduced graphene oxide (PRGO) decreased from 3.5-4.5 eV to 3.1-4.0 eV. Methanol vapour, which acts as a model VOC, was photodegraded using the PRGO. The effectiveness of the PRGO was mainly due to the removal of oxygen functional groups and restoration of the sp2 domain. This lowered the band gap and slowed down the electron recombination rate, which resulted in a higher photocatalytic activity. The photocatalytic activity of PRGO followed pseudo-first order kinetics, with a rate constant of 0.0025 min-1, and it could be reused for five cycles without any significant loss in the photocatalytic activity. This study demonstrates the potential of PRGO as a versatile and stable metal-free photocatalyst to remove indoor pollutants.

Optimization of toluene removal over W-doped TiO2 nano-photocatalyst under visible light irradiation

This study outlines the optimization of photocatalytic degradation of toluene by W-doped TiO₂ nanoparticles under visible light irradiation. Experiments were carried out based on the central composite design (CCD) methodology. W-TiO₂ nanoparticles were synthesized with various tungsten contents at different calcination temperatures by the sol-gel method. The nanoparticles' characteristics were determined using appropriate techniques such as field emission scanning electron microscopy, particle size analysis, X-ray diffraction and energy-dispersive spectroscopy. The effect of different operational conditions of coating mass, initial toluene concentration, and exposure time on the toluene removal efficiency was investigated. Result showed that tungsten has a fundamental role in improving the photocatalytic activity of TiO₂ under visible light, as well as improving its photoactivity under UV irradiation by decreasing the rate of electron/hole charge recombination. Analysis of the obtained data on toluene removal with a CCD approach illustrated that the quadratic model can effectively predict the toluene removal with coefficient of determination of R² = 0.862. Tungsten content and exposure time affect the toluene removal efficiency more than other factors. Results showed that maximum toluene removal efficiency slightly depends on the initial concentration of toluene. At the initial toluene concentration of 4000 ppm, the optimum values of the calcination temperature, tungsten content, coating mass, and exposure time were 500°C, 0.52 wt%, 11.7 g/m², and 8 h, respectively, with 59% removal of toluene.

A review on activated carbon adsorption for volatile organic compounds (VOCs)

A number of control methods have been adopted for the removal of hazardous volatile organic compounds (VOCs) from gas streams, particularly adsorption processes which are considered more prominent in terms of feasibility, effectiveness as well as cost competence compared to other methods. In this study, most of the activated-carbon-based adsorbents are critically reviewed in terms of their advantages and limitations for VOC gas adsorption. The choice of adsorbent and process parameters depends mainly on the type of VOC used, its chemical and structural properties, in addition to the adsorbent’s characteristics. The review discusses in detail the application of fixed-bed adsorption systems. A computational simulation study using quantum-chemical conductor like screening model for real solvents is included in this review which determines the efficiency in describing and predicting the adsorption technique required for each process. This review offers a comprehensive discussion of the VOC adsorption techniques and their implementation for different applications.

Effect of Doping Metals on the Structure of PEO Coatings on Titanium

The structure and properties of the oxide films formed on titanium alloys by means of plasma-electrolytic oxidizing in alkali electrolytes based on pyrophosphates, borates, or acetates of alkali metals with the addition of dopants’ oxides or oxoanions of varying composition have been studied. Anodic polarization in the spark discharge (microarc) mode at application of interelectrode potential 90 to 160 V has been used to obtain mixed-oxide systems TiOx·WOy, TiOx·MoOy, TiOx·ZrO2, and TiOx·V2O5. The possibility to obtain the oxide layers containing the alloying elements by the modification of the composition of electrolytes has been stated. The chemical and phase composition as well as the topography, the microstructure, and the grain size of the formed layers depend on the applied current, interelectrode voltage, and the layer chemical composition. The effect of formed films composition on the resistance of titanium to corrosion has been discussed. Catalytic activity of mixed-oxide systems was determined in the model reaction of methyl orange dye MO photodestruction.

Synthesis of TiO₂ with Hierarchical Porosity for the Photooxidation of Propene

The elimination of volatile organic compounds (VOCs) at low concentration is a subject of great interest because these compounds are very harmful for the environment and human health. In this work, we have developed a synthesis methodology of TiO₂ that allows obtaining meso-macroporous materials with hierarchical porosity and with high thermal stability for their application as photocatalysts in the removal of VOCs, specifically propene. The materials synthesized in this work were characterized by Scanning electron microscope (SEM), Transmission electron microscopy (TEM), powder X-ray diffraction (XRD), Thermogravimetric Analysis (TG), and nitrogen adsorption. It is observed that the samples calcined at 250 °C and 500 °C present a high photoactivity for the photooxidation of propene, which is similar to the benchmark material P25 (commercial TiO₂). Moreover, the textural properties are better than those for P25, indicating that the samples are interesting for the preparation of photocatalysts with different conformations, such as in the form of coatings and fillings in different size scales.

Photocatalytic performance of electrospun CNT/TiO2 nanofibers in a simulated air purifier under visible light irradiation

The photocatalytic treatment of gaseous benzene under visible light irradiation was developed using electrospun carbon nanotube/titanium dioxide (CNT/TiO₂) nanofibers as visible light active photocatalysts. The CNT/TiO₂ nanofibers were fabricated by electrospinning CNT/poly(vinyl pyrrolidone) (PVP) solution followed by the removal of PVP by calcination at 450 °C. The molar ratio of CNT/TiO₂ was fixed at 0.05:1 by weight, and the quantity of CNT/TiO₂ loaded in PVP solution varied between 30 and 60 % wt. CNT/TiO₂ nanofibers have high specific surface area (116 m²/g), significantly higher than that of TiO₂ nanofibers (44 m²/g). The photocatalytic performance of the CNT/TiO₂ nanofibers was investigated by decolorization of 1 × 10^-5 M methylene blue (MB) dye (in water solution) and degradation of 100 ppm gaseous benzene under visible light irradiation. The 50-CNT/TiO₂ nanofibers (calcined CNT/TiO₂ nanofibers fabricated from a spinning solution of 50 % wt CNT/TiO₂ based on PVP) had higher MB degradation efficiency (58 %) than did other CNT/TiO₂ nanofibers and pristine TiO₂ nanofibers (15 %) under visible light irradiation. The photocatalytic degradation of gaseous benzene under visible light irradiation on filters made of 50-CNT/TiO₂ nanofibers was carried out in a simulated air purifier system. Similar to MB results, the degradation efficiency of gaseous benzene by 50-CNT/TiO₂ nanofibers (52 %) was higher than by other CNT/TiO₂ nanofibers and pristine TiO₂ nanofibers (18 %). The synergistic effects of the larger surface area and lower band gap energy of CNT/TiO₂ nanofibers were presented as strong adsorption ability and greater visible light adsorption. The CNT/TiO₂ nanofiber prepared in this study has potential for use in air purifiers to improve air treatment efficiency with less energy.

Studies on adsorption, reaction mechanisms and kinetics for photocatalytic degradation of CHD, a pharmaceutical waste

The photocatalytic degradation of chlorhexidine digluconate (CHD), a disinfectant and topical antiseptic and adsorption of CHD catalyst surface in dark condition has been studied. Moreover, the value of kinetic parameters has been measured and the effect of adsorption on photocatalysis has been investigated here. Substantial removal was observed during the photocatalysis process, whereas 40% removal was possible through the adsorption route on TiO2 surface. The parametric variation has shown that alkaline pH, ambient temperature, low initial substrate concentration, high TiO2 loading were favourable, though at a certain concentration of TiO2 loading, photocatalytic degradation efficiency was found to be maximum. The adsorption study has shown good confirmation with Langmuir isotherm and during the reaction at initial stage, it followed pseudo-first-order reaction, after that Langmuir Hinshelwood model was found to be appropriate in describing the system. The present study also confirmed that there is a significant effect of adsorption on photocatalytic degradation. The possible mechanism for adsorption and photocatalysis has been shown here and process controlling step has been identified. The influences of pH and temperature have been explained with the help of surface charge distribution of reacting particles and thermodynamic point of view respectively.