TiO2 Composites Research Articles

Effect of TiO2 Morphology on the Properties and Photocatalytic Activity of g-C3N4/TiO2 Nanocomposites Under Visible-Light Illumination

This study focused on the preparation and investigation of g-C3N4/TiO2 photocatalysts using different TiO2 morphologies (anatase nanoparticles (TPs), poorly crystalline nanotubes (aTTs), and well-crystalline anatase nanorods (TRs)) and self-synthesized g-C3N4 (CN). The synthesis of the g-C3N4/TiO2 composites was carried out using a mortar mixing technique and a g-C3N4 to TiO2 weight ratio of 1:1. In addition, the g-C3N4/TiO2 composites were annealed in a muffle furnace at 350 °C for 2 h in air. The successful formation of a g-C3N4/TiO2 composite with a mesoporous structure was confirmed using the results of XRD, N2 physisorption, and FTIR analyses, while the results of microscopic analysis techniques confirmed the preservation of TiO2 morphology in all g-C3N4/TiO2 composites investigated. UV-Vis DR measurements showed that the investigated g-C3N4/TiO2 composites exhibited visible-light absorption due to the presence of CN. The results of solid-state photoluminescence and electrochemical impedance spectroscopy showed that the composites exhibited a lower charge recombination compared to pure TiO2 and CN. For example, the charge transfer resistance (RCT) of the CNTR/2 composite of TR and CN calcined in air for 2 h was significantly reduced to 0.4 MΩ, compared to 0.9 MΩ for pure TR and 1.0 MΩ for pure CN. The CNTR/2 composite showed the highest photocatalytic performance of the materials tested, achieving 30.3% degradation and 25.4% mineralization of bisphenol A (BPA) dissolved in water under visible-light illumination. In comparison, the pure TiO2 and CN components achieved significantly lower BPA degradation rates (between 2.4 and 11.4%) and mineralization levels (between 0.6 and 7.8%). This was due to (i) the presence of Ti3+ and O-vacancies in the TR, (ii) enhanced heterojunction formation, and (iii) charge transfer dynamics enabled by a dual mixed type-II/Z scheme mechanism.

Nano-sized heterogeneous photocatalyst Fe3O4@V/TiO2-catalyzed synthesis and antimycobacterial evaluation of 2-substituted benzimidazoles.

The 2-substituted benzimidazole has emerged as a promising heterocyclic compound in the field of drug design. In pursuit of more sustainable photocatalysts for 2-substituted benzimidazole synthesis, the method for coating Fe3O4 with V-doped TiO2 was presented. On the base of characterizing composition, morphology, and properties, the prepared nano-sized Fe3O4@V/TiO2 composites were used as a heterogeneous photocatalyst to catalyze the synthesis of 2-substituted benzimidazoles under light. The photocatalyst Fe3O4@V/TiO2 composites showed the enhanced photocatalytic activity compared to no V-doped Fe3O4@TiO2, being able to yield various 2-substituted benzimidazoles in moderate to good yield with recyclability and stability. A possible photocatalysis mechanism was investigated. It was evident that holes, singlet oxygen, and ·O2̄ radical played important roles in the synthesis of 2-substituted benzimidazole. Moreover, some of the obtained products were demonstrated excellent antibacterial activity.

Photocatalytic removal of synthetic dyes using Bi2O3–TiO2 nanocomposites obtained by simple hydrothermal route

This study describes the preparation of TiO2-modified Bi2O3 photocatalysts with different TiO2 contents, synthesized via an in situ hydrothermal method. The powder samples were characterized by XRD, SEM, TEM, FTIR–ATR, UV–Vis, XPS, and N₂ physisorption analysis. The photocatalytic activity of the TiO2-modified Bi2O3 was studied for the removal of methyl orange (MO) and methylene blue (MB) under different reaction conditions. The TiO2-modified Bi2O3 photocatalysts exhibited superior photocatalytic activity compared to the pristine samples of TiO2 and Bi2O3. The BiT16 sample achieved degradation rates of approximately 93.9% and 98.2% for MO and MB, respectively, within 120 min of reaction at 30 ppm. These results are attributed to the band gap values, differences in textural features, TiO2 content, and the reduction in the recombination process of e⁻/h⁺ pairs in the Bi2O3–TiO2 composites. Reaction kinetics were determined using the Langmuir–Hinshelwood mechanism, and during the third photoreaction cycle, the TiO2-modified Bi2O3 (BiT16) achieved photocatalytic degradation rates of 65.6% for MO and 70.5% for MB.

Loading of Ce and n co-doped TiO2 composites onto modified shell powder synergism of adsorption and photocatalysis phytic acid removal: performance and mechanism

Phytic acid was investigated as an organophosphorus pollutant. Titanium dioxide (TiO2) doped with Ce and N was prepared using the sol-gel method and loaded onto a modified shell power to produce modified shell powder/Ce-N-TiO2 (Msp/CeNT). The combined effects of adsorption and photocatalysis on phytic acid were explored. The actual phytic acid degradation rate with the composite photocatalyst was higher than the sum of the adsorption removal rate of phytic acid using the modified shell powder and the photocatalytic degradation removal rate of phytic acid using the Ce-N-TiO2 photocatalyst. Msp/CeNT synergistically affected adsorption and photocatalytic degradation. The effects of different factors, such as reaction temperature, catalyst dosage, initial pH, stirring speed, and light intensity, on the combined effect were investigated. The results showed that the synergistic effect increases with the increase of light intensity. Increasing the reaction temperature, catalyst dosage, initial pH, and stirring speed first increased and then decreased the synergistic effect of the composite photocatalysts. Phytic acid (69.54%) was degraded within 4 h when the temperature, pH, catalyst dosage, stirring speed, and light intensity were 25 °C, 5, 1 g/L, 300 rpm, and 500 W, respectively. We investigated and prepared a composite photocatalytic material, developing a new theoretical method for degrading organophosphorus dissolved in water and providing a basis for treating lake eutrophication as a practical application.

The photo-electrocatalytic property of hollow mesoporous graphene oxide/tungsten trioxide/titanium dioxide membrane photo-anode.

Titania (TiO2) is one of promising photo catalysts for its high ability to resistant photo corrosion and environmental friendliness, but its photocatalytic activity is too low to be used in industry. To find an approach to solve this problem, graphene oxide (GO), tungsten trioxide (WO3) and TiO2 composite with hollow mesoporous structure was prepared by a two-step spray drying method. The composite was used as raw material to constitute a membrane onto ITO glass to form a membrane photo-anode. In this way, its photo-electrocatalytic property was tested. The morphology, crystal phase, microstructure and specific surface area of the composite were characterized by SEM, XRD, TEM and BET, respectively. The surface potential distribution and optical property of the anode were measured by a Kelvin Probe Force Microscopy and a Fs-5 Steady-State Fluorescence Spectrometer, respectively. The forbidden bandwidth of the GO-WO3/TiO2 composite is 2.30eV, which is much lower than that of the WO3/TiO2 composite, 2.92eV. When the content of GO in the anode is around 1wt%, its light absorption ability is the best among all the anodes with different contents of GO, and its photocatalytic ability to degrade methyl orange is the strongest as our experiments concerned. These findings indicate that the addition of GO into the WO3/TiO2 composite can improve its photo-electrocatalytic property. The construction of membrane photo-anode is an efficient approach to solve the problem of the recovery and secondary utilization of nanoscale powder in water treatment.

Sulfur-doped g-C3N4/TiO2 anatase (101) composites for photocatalytic applications: a DFT-based computational investigation

With the aim of improving the visible-light photocatalytic activity of TiO2, the structural, electronic and optical properties of bare and sulfur-doped g-C3N4/TiO2 composites have been investigated as potential candidate materials.

Petrography and Geochemistry of Dolerite Dykes from Cretaceous Bamwa Half Grabben (North Cameroon, Central Africa)

Petrography and geochemistry of dolerite dykes from cretaceous Bamwa half grabben of North Cameroon in Central Africa have been done. Field work study have shown that dykes swarms of Bamwa basin exceptionally occurred as well exposed dykes vertically overhanging the local granitoids of the basement along trending direction of N155E. Dykes are 1 to 26 m wide and extend on 400 to 500 m. Microscopic observations have revealed various textures, from ophitic, sub-ophitic, classical dolerite to microlitic porphyritic. All dolerites are petrographically composed of plagioclase, oxides, clinopyroxene, rare apatite, chlorite and amphibole crystals, marked by alteration signs. ICP-AES and ICP-MS geochemical analyses of Bamwa dolerites have distinguished the dolerites lavas of basaltic trachyandesite, andesite, dacite and rhyolite composition. Bamwa dolerites are giant dykes which exhibit the geochemical characters of continental tholeiites of low TiO2 composition (TiO2 < 2 wt. %). Petrographic and geochemical studies of the dolerite dykes of Bamwa basin have shown that studied dolerites have experienced a complex petrogenetic history through assimilation and fractional crystallization, fluid infiltration and varying degrees of crustal contamination processes, after a relatively high partial melting rate of enriched subcontinental lithospheric mantle source. Studied dolerites stand as fingerprints of post Pan African magmatic events of arc-back arc setting after subduction.

Application of fly ash-TiO2 composites for enhanced adsorption and photocatalytic degradation of fuchsin dye.

It is important to accomplish both photocatalytic efficiency and adsorption capacity in the catalyst to produce a highly effective photocatalyst for complete dye removal from wastewater. In the current investigation, TiO2 and fly ash-TiO2 composites (0.5-5 wt%) were fabricated by sol-gel and wet-impregnation process, and their catalytic performance was evaluated for the effective adsorption and photocatalytic degradation of fuchsin blue dye. The catalysts were characterized by XRD, UV-DRS, SEM, EDS, RAMAN spectroscopy, and N2 adsorption analysis Adsorption and degradation studies were conducted to investigate factors such as pH (2 - 10), adsorbent dose (1-9mg), contact time (30-180min), and initial adsorbate concentration (5-30mg/L) to eradicate fuchsin dye from water. The 5 wt% fly ash-TiO2 catalyst showed a maximum capacity for adsorption of 20.32mg/g and 76% removal of fuchsin dye. The Langmuir isotherm model fitted well to the experimental data, whereas the adsorption process obeyed pseudo-first-order kinetics. When exposed to UV light, a 5 wt% fly ash-TiO2 composite demonstrated maximum photocatalytic degradation of 88% after 180min, followed by a pseudo-first-order kinetic model. The catalyst was easily reusable for five cycles without losing dye removal effectiveness.

The Quality Study of Hydroxyapatite (HAp)-TiO2 Composites from Pokea (Batissa violacea var. celebensis) Shell Waste by Hydrothermal, Microwave and Precipitation Methods

Research on the quality study of hydroxyapatite (HAp)-TiO2 composites from Pokea (batissa violacea var. celebensis) clamshell waste by hydrothermal, microwave and precipitation methods have been successfully conducted. This study aims to determine the characteristics and quality of HAp-TiO composites2 synthesized from Pokea clam shell using three different methods, namely hydrothermal, microwave and precipitation. FTIR characterization showed the absorption of PO4-3 functional groups in the wave number range 567-1091 cm-1, -OH and -NH groups at wave numbers 3444-3448 cm-1, and Ti-O groups at 567-632 cm-1. XRD analysis revealed a diffraction pattern at 2θ = 26.67o, with crystal sizes of HAp-TiO2 material of 80.20 nm, 71.47 nm, and 73.28 nm for hydrothermal, microwave and precipitation methods, respectively. The mechanical properties showed that the highest compressive strength of the HAp-TiO2 composite was obtained in the hydrothermal method (6.07 MPa), followed by the precipitation method (5.19 MPa) and microwave (5.08 MPa). The material density test results for the hydrothermal, microwave and precipitation methods were recorded at 2.27 MPa, 2.12 MPa, and 1.73 MPa. The test results showed the highest value in the hydrothermal method of 24.24 MPa, while the microwave and precipitation methods produced hardness of 18.61 and 18.83 MPa, respectively. Digital optical microscope analysis showed the surface morphology of the material to be uniform, refined grains with pores. The results in this study indicate that the hydrothermal method produces composites with better mechanical quality and crystal structure than other methods.

(Invited) TiO2/MWCNT Composite Photoelectrodes for Water-Splitting Reaction Prepared Via Sol–Gel Electrophoretic Deposition

TiO2 is a representative photocatalyst used in practical applications. To improve its catalytic activity, an increase in the active surface area and electroconductivity is a promising approach. For this purpose, various composite structures have been investigated by many researchers. We investigated the composition of TiO2 with multi-walled carbon nanotubes (MWCNT) using various approaches. Recently, we have developed on environmentally-friendly sol–gel electrophoretic deposition (sol–gel EPD) to find the best composite structures of TiO2 and MWCNT as a photoanode.[1] Consequently, it was demonstrated that sol–gel EPD produces various film structures by changing the deposition conditions. For example, it was confirmed that the solute composition, that is, the proportion of TiO2 sol to MWCNT in the electrophoresis bath, linearly changed the thickness and Ti/C composition of the film. Excellent photoelectrochemical activity for the water-splitting reaction was confirmed with a TiO2 film by combining MWCNT in an appropriate manner via sol–gel EPD to improve the film conductivity and UV adsorption by TiO2. In this presentation, several conditions including solvent as well as solute composition of sol–gel EPD significantly influencing film structures of TiO2/MWCNT composite films will be introduced, and the as-prepared film structures that show the best photoelectrochemical activity are also discussed.[1] Matsunaga, Y. Yu, K.Takahashi, “Photoelectrochemical Activity of TiO2/MWCNT Thin-Film Electrodes with Different Film Structures Prepared by Combining Electrophoretic Deposition and Sol–Gel Method,” Electrochemistry, 92(4), 047004 (2024).

Enhancing membrane performance for oily wastewater treatment: comparison of PVDF composite membranes prepared by coating, blending, and grafting methods using TiO2, BiVO4, CNT, and PVP

This comparative study investigates the modification of polyvinylidene fluoride (PVDF) membranes with different nanoparticles (TiO2 or TiO2-based composites containing BiVO4 and/or CNT), using three distinct methods (blending, coating, and grafting) and polyvinylpyrrolidone (PVP). The objective was to enhance the photocatalytic and filtration performance for the separation of oil-in-water emulsions. Regarding the UV activity, the PVDF-TiO2/CNT/PVP-coated membrane presented the best performance. Overall, the addition of 2 wt.% CNT to the TiO2 notably enhanced the photocatalytic activity of the membranes for both UV and visible irradiations. Meanwhile, the presence of 2 wt.% BiVO4 was beneficial only for photocatalysis under visible light irradiation. Regarding the filtration of the oil-in-water emulsions, 2 wt.% CNT or BiVO4 addition resulted in the highest fluxes in the series of the PVDF-TiO2-grafted membranes. The presence of pore former PVP led to relatively high fluxes and photocatalytic activities for all series. Regarding the modification methods, coated membranes showed the highest photocatalytic efficiency and lowest fluxes. Grafted membranes showed relatively high photocatalytic efficiencies and the best filtration performances.

Visible light sensitive BiVO4–TiO2 nanocomposites for photocatalytic dye degradation

Abstract The hydrothermal approach was used to prepare visible light active BiVO4–TiO2 nanosheet composites in varying molar ratios. The photoluminescence (PL) spectrum, X-ray photoelectron spectroscopy (XPS), UV-Visible Diffuse Reflectance Spectroscopy (DRS), Transmission electroscopy (TEM), Brunauer-Emmett-Teller (BET) and field emission scanning electron microscopy (FESEM), were used to analyze the photocatalysts and composites. Photocatalytic activity of BiVO4–TiO2 composites was investigated by decolorizing methylene blue. Out of four different molar ratio BiVO4–TiO2 composites with a molar ratio of 3:1 BiVO4 TiO2 composite showed enhanced photocatalytic activity which is further proved by photoluminescence investigation of coumarin and Scavenger test. The DRS of BiVO4 TiO2 composite showed red shift in optical absorption. The enhanced photocatalytic activity is due to minimizing electron hole recombination by making composite with TiO2.

Looped In Lupus-An Unusual Manifestation

Systemic Lupus Erythematosus (SLE) is a chronic autoimmune disorder that can involve the central nervous system (CNS) in 40-70% of cases. Neuropsychiatric SLE presenting as parkinsonism is rare. We present a case of a 39-year-old woman who initially presented with polyarthritis and fever, followed by difficulty walking and speech impairment. Examination revealed an expressionless face, low-volume speech, resting tremors, and limb rigidity without cerebellar or sensory deficits. Investigations revealed ANA positivity, elevated anti-dsDNA and anti-Sm antibodies, proteinuria, and multiple brain infarcts. The patient was treated with Methylprednisolone, Levodopa, and Hydroxychloroquine, showing clinical improvement. Physicians should suspect SLE in patients with parkinsonism and polyarthralgia, as vasculopathy due to impaired thalamostriate arteries may contribute to parkinsonism.

Impression creep behavior of extruded Mg–TiO2 composites prepared by powder metallurgy

Magnesium (Mg) composites with ceramic fillers are considered favorable for their recyclability compared to Mg alloys for lightweight designs with high creep resistance. In this work, we studied the difference in impression creep properties of pure magnesium and its composites, which contained 2, 3.5, and 5 vol% of submicron TiO2 particles. For each composition, samples were fabricated by hot extrusion after hot pressing of the cold-compacted powders. Creep tests were conducted at temperatures in the 423–473 K range and under stress levels in the 125–275 MPa range. The results showed that the composites had higher creep resistance than pure magnesium, and increasing TiO2 content improved their creep behavior under all testing conditions. The effect of TiO2 content on grain size was statistically insignificant, and therefore, the improvement was attributed to reinforcing ceramic particles, which reduce the creep load on the magnesium matrix. The Dorn model was used in a new approach to calculate the effective stress on the magnesium matrix, justifying composites' higher creep load-bearing capacity than pure Mg under studied creep conditions. Fitting the Dorn exponential equation to creep data revealed that the stress exponent was between 6.6 and 8.6, and the activation energy was between 90.1 and 95.2 kJ/mol for all compositions. Therefore, it was inferred that pipe diffusion-controlled dislocation climb was the creep mechanism for the studied materials.

Synthesis and Characterization of TiO2 Thin Films Modified with Anderson-Type Polyoxometalates (Ni, Co, and Fe)

In this work, TiO2 and Anderson-type polyoxometalates (Ni, Co, and Fe) thin-film composites were fabricated. The composites were characterized by FTIR and Raman spectroscopy, diffuse reflectance, and scanning electronic microscopy. The methylene blue (MB) photocatalytic degradation on the composites under UV irradiation was studied. Spectroscopic results verified the modification of TiO2 thin films. Optical and morphological properties changed after TiO2 modification. The largest change in the optical band gap was observed for the FePOM/TiO2 system, which reported a value of 3.05 eV. The POM/TiO2 systems were more efficient in methylene blue (MB) adsorption than bare TiO2. Furthermore, the modified films were more efficient than bare TiO2 during MB photodegradation tests. The NiPOM/TiO2 and the CoPOM/TiO2 were the most efficient in the MB adsorption, reaching ~20%. The NiPOM/TiO2 and the CoPOM/TiO2 composites were the most efficient in the photodegradation process, reaching ~50% of MB removal. The stability tests indicated that composite films were moderately stable after the three performed reusability cycles. Thus, these results suggest that POM modification of TiO2 can improve the adsorption and photodegradation capacity of semiconductors.

Dual quenching ECL strategy based on AgInZnS quantum dots and a new co-reaction promoter oxygen vacancy-modified P5AIn/TiO2 for sensitive CEA detection

A novel electrochemiluminescence (ECL) biosensor for the sensitive detection of carcinoembryonic antigen (CEA) was constructed, utilizing environmentally friendly AgInZnS quantum dots (AgInZnS QDs) and a new co-reaction promoter enriched with oxygen vacancies, namely titanium dioxide/poly(5-aminoindole) (Ov-TiO2/P5AIn). The composite of P5AIn and TiO2 significantly enhanced the reaction rate of AgInZnS QDs with tripropylamine (TPrA). In addition, the presence of oxygen vacancies significantly enhances the electron migration rate of the electrode material, leading to more efficient catalysis of TPrA+ generation and a significant enhancement of ECL signals. Furthermore, a dual-quenching sensing strategy was employed using cuprous oxide-triaminophenol (Cu2O@APF) as the quencher, enabling the biosensor to switch. Through dual quenching of the ECL emission from AgInZnS QDs by Cu2O and APF, the biosensor achieves an extremely low “off” state of the ECL signal. Furthermore, a signal amplification strategy driven by the synergistic action of exonuclease III (ExoIII) and restriction endonuclease (Nt.BbvCI) was designed for a dual-site DNA walker, achieving cyclic amplification of the target signal and ECL signal, thereby turning the signal “on” again. The above mechanism significantly improved the specificity and sensitivity of the biosensor for CEA detection. The prepared biosensor exhibits good stability, selectivity, and sensitivity. The linear range for CEA detection is 5 × 10−14 to 10−8 M, with a detection limit of 16 fM. Additionally, the biosensor demonstrates satisfactory analytical capability for CEA in real blood samples. This strategy provides a reliable new approach for the sensitive detection of CEA and other tumor markers.

Optimization of Hydrogen Utilization and Process Efficiency in the Direct Reduction of Iron Oxide Pellets: A Comprehensive Analysis of Processing Parameters and Pellet Composition

The article deals with the H2 consumption for different processing conditions and the composition of the processed pellets during the direct reduction process. The experiments are carried out at 600–1300 °C, with gas pressures of 1–5 bar, gas flow rates of 1–5 L min−1, and basicity indices of 0 to 2.15. Pellets with different compositions of TiO2, Al2O3, CaO, and SiO2 are analyzed. The gas flow rate is crucial, with 0–10 L min−1 leading to an H2 consumption of 0–5.1 kg H2/kg pellet. The gas pressure (0–10 bar) increases the H2 consumption from 0 to 5.1 kg H2/kg pellet. Higher temperatures (600–1300 °C) reduce H2 consumption from 5.1 to 0 kg H2/kg pellet, most efficiently at 950–1050 °C, where it decreases from 0.22 to 0.10 kg H2/kg pellet. An increase in TiO2 content from 0% to 0.92% lowers H2 consumption from 0.22 to 0.10 kg H2/kg pellet, while a higher Fe content (61–67.5%) also reduces it. An increase in SiO2 content from 0% to 3% increases H2 consumption from 0 to 5.1 kg H2/kg pellet. Porosity structure influences H2 consumption, with the average pore size decreasing from 2.83 to 0.436 mm with increasing TiO2 content, suggesting that micropores increase H2 consumption and macropores decrease it.

Synergistic photocatalytic degradation of methylene blue using TiO2 composites with activated carbon and reduced graphene oxide: a kinetic and mechanistic study

This comprehensive study explored the removal of methylene blue (MB) from aqueous solutions as a model pollutant, utilizing solar-driven photocatalysis with nano-sized titanium dioxide (TiO2) and composites with activated carbon (AC) and reduced graphene oxide (RGO). This research introduces continuous solar reactor instead of conventional batch experiments investigating its design configuration. Utilizing response surface methodology (RSM), the study determined the optimal process conditions (MB concentration at 30 mg/L, pH 8.82, irradiation time 138 min), under which TiO2 achieved a 93.13% MB removal efficiency. The study further revealed that the integration of TiO2 with AC and RGO (5% wt.) significantly enhanced the MB photocatalytic degradation. The TiO2/AC composite achieved 98.3% MB degradation in 138 min of solar exposure, related to its large specific surface area of 146 m2/g and a pore volume of 0.439 cm3/g. Likewise, the TiO2/RGO composite demonstrated 97% removal with a surface area of 102 m2/g and a pore volume of 0.476 cm3/g, significantly better than nano-TiO2. Additionally, the research investigated the role of the solar reactor configuration on MB removal. Using 26 mm Pyrex tube diameter with 15 cm long on parabolic aluminum concentrator inclined at 30° optimally achieved the peak MB degradation efficiency. Recyclability tests shown a noticeable decrease in nano-TiO2 efficiency to 56.03% without regeneration; however, after regeneration following the third cycle, the efficiency significantly recovered to 70.07%. Thereby, this paper introduces an innovative, continuous, and well-designed solar reactor system for dye removal, employing nano-TiO2 and its composites with AC and RGO for improved photocatalytic efficiency under statistically optimized process conditions.

Composite photocatalysts g-C<SUB>3</SUB>N<SUB>4</SUB>/TiO<SUB>2</SUB> for hydrogen production and dye decomposition

The photocatalytic activity of the g-C3N4 /TiO2 composite samples in the processes of dye (methylene blue) decomposition and hydrogen evolution from an aqueous ethanol solution under the action of visible radiation (400 nm) has been studied. A new original method for the synthesis of the g-C3N4 /TiO2 composite by depositing g-C3N4 /TiO2 to TiO2 nanoparticles during sol-gel synthesis is proposed. The synthesized photocatalysts were characterized by X-ray diffraction, low-temperature gas adsorption, X-ray photoelectron spectroscopy, high-resolution transmission microscopy, and diffuse reflectance spectroscopy in the UV and visible regions. The maximum activity in the hydrogen evolution reaction was 1.3 mmol h–1, which exceeds the rate of hydrogen evolution on the unmodified g-C3N4 and TiO2 samples.

An insight into PANI-TiO2 photocatalysis of refractory organic matter through molecular size fractionation.

Refractory organic matter (RfOM) is ubiquitous in aquatic environment and plays various roles in regulating the fate, transport, toxicity, and bioavailability of chemical species, such as metals, emerging organic contaminants, and nanomaterials. RfOM is mainly represented by humic acids (HA) as the acid insoluble fraction of organic matrix. Considering the complex and multicomponent characteristic of HA, a detailed study was designed to elucidate the fate of molecular size fractions (MSFrs) of humic under solar irradiation in the presence of polyaniline (PANI)-modified TiO2 composites. Humic acid as a consortium of diverse molecular size fractions with different tendencies towards oxidation requires further assessment by UV-vis and fluorescence spectroscopic parameters complementary to previous studies on the photocatalytic degradation of RfOM by using TiO2 and PANI-TiO2 composites. Absorbance-based removal efficiencies under initial and post-photocatalytic conditions showed a re-formation trend during photocatalysis in the presence of PANI and TiO2 where higher MSFrs were transformed to lower MSFrs that was apparent for < 3kDa fraction. Completely different profiles were observed for PT-41 and PT-81 indicating similar degradation pathways independent of PANI ratio in the composite. As confirmed by the investigated parameters, formation of both 450kDa and 220kDa MSFrs were evident under all conditions indicating in situ generation of higher MSFrs. The eligibility of coupled absorbance-fluorescence measurements to discern molecular size distribution of humic acid via oxidative degradation was also investigated. Excitation-emission matrix (EEM) contour plots emphasized the ratio dependency of PANI modification of TiO2 and revealed sample specific variations that were more pronounced in terms of the emergence of tyrosine- and tryptophan-like aromatic proteins.