Photocatalytic Activity Of TiO2 Research Articles

Remediation of methylene blue water solution with iodine doped TiO2 nanoparticles and their regeneration: For reuse and check phytotoxicity level of treated water

Titanium dioxide (TiO2) is an essential metal-oxide semiconductor with unique features, such as low cost, photostability, nontoxicity, and abundance used as a photocatalyst. However, TiO2's photocatalytic activity is limited because it exclusively absorbs incoming light in the ultraviolet (UV) range. In present work, Iodine-doped TiO2 (IDT) photocatalysts were prepared employing solution-combustion process in various mol % of iodine (I), i.e., Ti1-xIxO2 (x = 0.00–0.05). Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and UV–Vis Diffuse Reflectance spectroscopic (DRS) were used to characterise the synthesised IDT. DRS indicated that iodine doping increased the absorbance range while diminishing its bandgap energy. As the I doping concentration in TiO2 increased, there was a constant shift in absorbance towards the visible light area. The XRD demonstrated that the prepared photocatalysts were solely with the anatase phase of TiO2. The FTIR identified the functional groups in the prepared photocatalysts and numerous Ti–O lattice stretching and bending vibrational bands. Photocatalytic degradation of methylene blue (MB) dye was tested in a UV photochemical reactor. The 3 % IDT photocatalyst has the highest photodegradation efficiency amid all the prepared pristine and IDT photocatalysts. Regarding dye photodegradation, the synthesised TiO2 photocatalyst doped with 3 % Iodine outperformed the commercially available Aeroxide P-25 photocatalyst. Furthermore, the nanoparticles demonstrated excellent reusability in regeneration trials. A study on the germination of "Vigna Radiata" was done to determine phytotoxicity as part of the investigation into the potential use of photocatalytically treated water in irrigation. The phytotoxicity evaluation results show that the treated water has potential for use in irrigation.

Investigating for Photocatalytic Activity of Hybrid TiO2/Reduced Graphene Oxide and Application in Reducing VOCs

In this study, rGO/TiO2 hybrid nanostructures (rGO : reduced Graphene Oxide) have been successfully fabricated for the purpose of application in the treatment of volatile organic compound (VOCs) that harmful for the environment through the method of directly measuring the change in concentration of decomposed VOCs in real time under UV-excited conditions using a home-made measuring system. the results showed that hybrids TiO2 : rGONFs (reduced Graphene Oxide nano flake) samples with the weight ratio between two kind of material are 99%:1% and 98%:2% which reduced VOCs faster than 2 time intrinsic TiO2. The phenomenon of 2D materials involved in the hybrids lead to the fact that the photocatalytic activity of TiO2 had been significantly improved, this can be explained as follows: When heterogeneous hybrid was formed, because of the difference in energy levels of conduction band between two materials was negligible, heterojunction barrier is not too high this made the photogenerated electrons from TiO2 easily move through rGONFs under UV stimulation. This thing has significantly reduced the recombination of the generated carrier in TiO2 during irradiation, which lead to an increase in the lifetime of the carrier and make photocatalytic reaction of the assembly become more effective. Copyright © 2024 by Authors, Published by BCREC Publishing Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

Structural Properties and Photocatalytic Activity of TiO2/Au Nanocomposites Synthesized with Glucose

AbstractA one‐pot synthesis of plasmonic gold‐modified TiO2 nanocomposites is reported by using glucose reduction of HAuCl4 in presence of titanium tetraisopropoxide. The resulting nanocomposites are characterized by thermal‐gravimetric analyses, X‐ray diffraction combined with X‐ray fluorescence and photoelectron spectroscopies. A binary system of β‐TiO2 and anatase phases is obtained for low Au content while only anatase form is favored when the initial Au rate rises. This investigation also suggests the inclusion of gold in the TiO2 structure. Although the optical bandgap of the different nanocomposites remains around 3 eV, the increase of Au content induces a shift of both valence and conduction edge bands to lower energy levels. The photocatalytic activity of TiO2/Au nanocomposites is assessed through the decolorization of different cationic and anionic dyes as model compounds. Regarding rhodamine and methylene blue dyes, the sample TiO2 modified with 3.5 wt% of Au presents the best performance. The relation between the structure of the nanocomposites and their capacity to degrade pollutants is discussed.

Bimetallic CuCo nanoparticles optimized hydrogen generation active centers thereby significantly enhancing TiO2 photocatalytic activity

Bimetallic nanostructures are currently a hot pot material among many hydrogen generation co-catalysts. In this study, CuCo bimetallic nanostructures were formed by introducing Co into Cu as the co-catalyst for TiO2. Characterization results from XRD, XPS, and TEM indicated the successful preparation of the high-crystallinity, impurity-free CuCo/TiO2 photocatalyst, with CuCo bimetallic nanoparticles uniformly dispersed on TiO2. After the addition of Co, density functional theory (DFT) calculations showed that the free energy of H adsorption on the Cu site was optimized from 0.27 eV to −0.56 eV, which was beneficial for hydrogen production from TiO2. Electrochemical characterization, photoluminescence (PL) spectroscopy, infrared (IR) thermography, and finite difference in time domain (FDTD) results showed that the bimetallic CuCo acted as the co-catalyst, which increased the temperature of the reaction system, facilitated the separation of light-generated electron-hole pairs, and accelerated the charge transfer, thus promoting the photocatalytic hydrogen generation. The findings of the photocatalytic performance demonstrate that the photocatalyst exhibits the H2 generation rate of 1933.8 μmol/g/h, which is approximately 9 times greater than that of pure TiO2 (213.4 μmol/g/h), when the bimetallic CuCo is loaded in the molar ratio of 5:5 and at the loading amount of 2 wt%. Additionally, the photocatalyst demonstrated excellent catalytic stability, reaching 87.1% of the initial after 16 h of cycling tests. It is foreseen that further study and optimization of various metal couplings may enable the larger widespread application of bimetals as co-catalysts for hydrogen generation.

Efficient photocatalytic hydrogen generation by CeCO3OH/TiO2 composites

Due to its low photogenerated carrier separation efficiency and wide band gap, the photocatalytic activity of TiO2 is not ideal. In this work, CeCO3OH/TiO2 composites were successfully prepared by a simple hydrothermal method. A series of characterisations shows that the CeCO3OH/TiO2 composites improves the photogenerated carrier separation efficiency, narrowes the band gap width and increases the visible light absorption capacity compared with the monomer, enhancing the photocatalytic hydrogen evolution performance. Under visible light irradiation, 20% CeCO3OH/TiO2 exhibites the highest photocatalytic hydrogen production performance of 2386.16 μmol g−1 h−1, which is 18.7 times higher than that of pure TiO2 and 25.8 times higher than that of pure CeCO3OH. It provides ideas for the development of more efficient photocatalytic materials and technologies.

Crystal surfaces cooperate with F ion migration to improve the photocatalytic performance of Z-type Ag-Ag2S/F-TiO2 composites

The TiO2 has the problems of low utilization of visible light and high photogenerated carrier recombination rate. The photocatalytic activity of TiO2 can be significantly improved by introducing F ion and narrow band gap material Ag2S. When F ions are present on the {001} surface of TiO2, surface F ions drive positively charged holes across the {001} surface, creating a synergistic effect that promotes the separation of electron-hole pairs. During the sample composite process, a certain amount of Ag will be precipitated to form an all-solid Z-type heterojunction structure of Ag2S, Ag and F-TiO2, which can improve the electron-hole separation efficiency. The results of XPS characterization confirmed the migration of F ion and the precipitation of Ag. The Ag2S/F-TiO2 composite sample was referred to as AT for short, and the corresponding ratio was 1:10,1:20,1:30,1:40, the optimal sample AT 1:20 degraded 95.6% tetracycline hydrochloride within 2 hours. This work simultaneously realizes TiO2 self-modification (synergistic effect of F ion migration and TiO2{001} crystal surface) and composite modification (formation of all-solid Z-type heterojunction), a new idea of studying TiO2 self-modified cooperative heterostructures is proposed, and the good application potential of AT nanocomposites in photocatalytic water treatment technology is demonstrated.

Microwave-assisted Synthesis and Photocatalytic Activities of TiO 2 Nanoparticles

Microwave-assisted Synthesis and Photocatalytic Activities of TiO ₂ Nanoparticles

Gas-Phase Fabrication and Photocatalytic Activity of TiO2 and TiO2-CuO Nanoparticulate Thin Films.

CuO-loaded TiO2 nanomaterials have applications in pollutant degradation via photocatalysis. However, the existing methods of fabricating these nanomaterials involve liquid-phase processes, which require several steps and typically generate liquid waste. In this study, TiO2 and TiO2-CuO nanoparticulate thin films were successfully fabricated through a one-step gas-phase approach involving a combination of plasma-enhanced chemical vapor deposition and physical vapor deposition. The resulting films consisted of small, spherical TiO2 nanoparticles with observable CuO on the TiO2 surface. Upon annealing in air, the TiO2 nanoparticles were crystallized, and CuO was completely oxidized. The photocatalytic activity of TiO2-CuO/H2O2, when introduced into the rhodamine 6G degradation system, was substantially enhanced under both ultraviolet and visible light irradiation. Moreover, this study highlights the influence of pH on the photocatalytic activity; TiO2-CuO/H2O2 exhibited the highest photocatalytic activity at pH 13, with a reaction rate constant of 0.99 h-1 cm-2 after 180 min of visible light irradiation. These findings could facilitate the development of nanoparticulate thin films for enhanced pollutant degradation in wastewater treatment.

The effects of water, substrate, and intermediate adsorption on the photocatalytic decomposition of air pollutants over nano-TiO2 photocatalysts.

The photocatalytic performance of nano-TiO2 photocatalysts in air pollutant degradation greatly depends on the adsorption of water, substrates, and intermediates. Especially under excessive humidity, substrate concentration, and intermediate concentration, the competitive adsorption of water, substrates, and intermediates can seriously inhibit the photocatalytic performance. In the past few years, extensive studies have been performed to investigate the influence of humidity, substrate concentration, and intermediates on the photocatalytic performance of TiO2, and significant advances have been made in the area. However, to the best of our knowledge, there is no review focusing on the effects of water, substrate, and intermediate adsorption to date. A comprehensive understanding of their mechanisms is key to overcoming the limited application of nano-TiO2 photocatalysts in the photocatalytic decomposition of air pollutants. In this review, the progress in experimental and theoretical fields, including a recent combination of photocatalytic experiments and adsorption and photocatalytic simulations by density functional theory (DFT), to explore the impact of adsorption of various reaction components on nano-TiO2 photocatalysts is comprehensively summarized. Additionally, the mechanism and broad perspective of the impact of their adsorption on the photocatalytic activity of TiO2 in air treatment are also critically discussed. Finally, several solutions are proposed to resolve the current problems related to environmental factors. In general, this review contributes a comprehensive perspective of water, substrate, and intermediate adsorption toward boosting the photocatalytic application of TiO2 nanomaterials.

Evaluating the energy consumption, structural, and corrosion resistance properties of photocatalytic TiO2-based PEO coatings on pre-anodized AA2024-Al

In this work, a thorough investigation is carried out to develop plasma electrolytic oxidation (PEO) coatings on pre-anodized AA2024-Al at various concentrations of TiO2 dispersed in a water base electrolyte of sodium silicate, sodium phosphate dodecahydrate, and potassium hydroxide in order to determine the effect of TiO2 incorporation on energy consumption, coating growth, surface morphology, photocatalytic behavior, and associated long-term corrosion resistance properties. The pre-anodization time is controlled to develop a 20.0 ± 1.6 µm thick anodic film, where a reduction of ∼66 % in the energy consumption (kW h m2 µm−1) is observed compared to the PEO developed without pre-anodic precursors, while the addition of TiO2 nanoparticles (Degusa-P25) into the base electrolyte results in reductions of ∼68 %, 64 %, and 51 % for the PEO coatings developed at 2, 5 and 10 g/L TiO2-based electrolyte, respectively. TiO2-based PEO process is found to improve growth rate, coating microstructure with lower porosity and defects, and reduce energy consumption (for a coating of a given thickness). The photocatalytic activity of TiO2 was investigated by photodegrading phenol under simulated sunlight conditions, where the higher concentration of TiO2 nanoparticles affected the phenol photodegradation efficiency, whereas the effectiveness of TiO2 concentration on the corrosion resistance properties of PEO coatings was observed with nearly one-order higher impedance magnitude (after 336 h) than the PEO layer without TiO2.

Effect of carbon nanotube incorporation on the photocatalytic activity of TiO2 nanotubes

Arrays of titanium dioxide (TiO2) nanotubes were prepared on commercially pure titanium (Ti) foils by anodic oxidation in a 0.5 M hydrofluoric acid (HF)-based electrolyte with multiwalled carbon nanotubes (MWCNTs) up to 0.035 g/l. The samples were annealed at 450°C for 1 h after anodic oxidation to form a crystalline anatase structure. The effect of MWCNT addition on the morphology and photocatalytic activity of the nanostructures was characterized by scanning electron microscopy, Raman spectroscopy, ultraviolet–visible diffuse reflectance spectroscopy, photoluminescence spectroscopy and methylene blue degradation tests. The results showed that MWCNTs were successfully incorporated into the titanium dioxide nanotube structure and significantly affected its photocatalytic activity. The best photocatalytic performance was achieved with the use of 0.025 g/l MWCNTs in the electrolyte composition. However, when the MWCNT content in the electrolyte increased, the electron–hole recombination rate and photon absorption ability of the structure deteriorated, resulting in a decreased photocatalytic activity.

Traces of Potassium Induce Restructuring of the Anatase TiO2(001)-(1×4) Surface from a Reactive to an Inert Structure.

Reconstruction of solid surfaces is generally accompanied by changes in surface activities. Here, via a combined experimental and theoretical study, we successfully identified that a trace amount of potassium dopant restructures the mineral anatase TiO2(001) single-crystal surface from an added molecule (ADM) termination to an added oxygen (AOM) one without changing the (1×4) periodicity. The anatase TiO2(001)-(1×4)-ADM surface terminated with 4-fold coordinated Ti4c and 2-fold coordinated O2c sites is (photo)catalytically active, whereas the anatase TiO2(001)-(1×4)-AOM surface terminated with O2c and inaccessible 5-fold coordinated Ti5c sites is inert. These results unveiled a mechanism of dopant-induced transformation from a reactive to an inert TiO2(001)-(1×4) surface, which unifies the existing arguments about the surface structures and (photo)catalytic activity of anatase TiO2(001)-(1×4).

Photocatalytic degradation of alkyl imidazole ionic liquids by TiO2 nanospheres under simulated solar irradiation: Transformation behavior, DFT calculations and promoting effects of alkali and alkaline earth metal ions

In this study, TiO2 nanospheres prepared by the sol-gel method were found to efficiently catalyze the photodegradation of 1-butyl-2,3-dimethylimidazolium bromide salt ([BMMIm]Br) under simulated solar irradiation through the main attack of hydroxyl radicals (•OH). The promoting effect of alkali metal (Li+→Cs+) and alkaline earth metal ions (Mg2+→Ba2+) was particularly emphasized. In-situ EPR tests showed that the introduction of alkali and alkaline earth metal ions could enhance the formation of •OH thus leading to a 7%−30.3% increase in the degradation efficiency of. [BMMIm]+. Moreover, the removal efficiency of [BMMIm]+ still reached > 96.19% in four real waters. A total of 23 products of [BMMIm]Br were detected, and hydroxyl substitution, bond breaking, direct oxidation and ring opening were considered as the main reactions during the photocatalytic degradation process. The results of toxicity evaluation showed that hydroxylation was a reaction process of increasing toxicity, while the bond breaking reaction had great detoxification capacity for [BMMIm]+. These findings may enhance our understanding on the effects of alkali or alkaline earth metal ions on the photocatalytic activity of TiO2, which could also provide reference for the efficient and green removal of alkylimidazolium ionic liquids in waters.

Fabrication of sputter coated Cu impregnated TaO[sbnd]NbO composite: A synchronized scavenging photocatalyst for water purification

Synchronized scavenging photocatalysts are needed for water purification due to the increasing demand for clean and safe water resources. The presence of organic pollutants and microorganisms in water sources can pose a significant risk to human health and the environment. This study compared the photocatalytic activity of the sputter-coated TaONbO and Cu-impregnated TaONbO/Cu nanocomposite with TiO2 (Degusa P-25) under solar radiation. The TaONbO/Cu and TaONbO nanocomposites crystallinity, structure and defects of composite, surface morphology, elemental composition and chemical state of material were evaluated by XRD, HRTEM, SEM, and XPS, respectively. Photoluminescence (PL) studies were employed to analyze the optical properties of the photocatalyst. The photocatalytic activity of TiO2, TaONbO/Cu and TaONbO was evaluated under solar radiation using P-Rosaniline Hydrochloride (PRH-Dye) as a model contaminant. IC and GC–MS were used to track the mineralized byproducts and intermediates produced during PRH-Dye degradation. The sputter-coated TaONbO/Cu photocatalyst was reused for up to 5 cycles, and no change in reaction kinetics was observed. This clearly indicates that TaONbO/Cu can be reused for several cycles. Using sputter-coated TaONbO/Cu photocatalysts enhanced performance compared to TiO2 and TaONbO. Using sputter-coated TaONbO/Cu photocatalysts to remove organic contamination from drinking water under solar radiation is a promising technology that can be a game-changer in the field of water treatment.

Enhanced photocatalytic performance of W-doped TiO2 nanoparticles for treatment of Procion Red MX-5B azo dye in textile wastewater

Sol-gel synthesis of W-doped TiO2 nanoparticles (W-TiO2) as a photocatalyst for Procion Red MX-5B (MX-5B) azo dye treatment in textile wastewater was the main focus of this research. Scanning electron microscopy (SEM), X-ray diffractometer (XRD), X-ray photoelectron spectroscopy (XPS), and energy dispersive spectroscopy (EDS) structural studies of nanostructured photocatalysts showed that W was successfully incorporated into the TiO2 lattice. According to EIS investigations, W-TiO2 has a greater rate of charge transfer and excellent charge separation capabilities compared to a sample of pure TiO2. It shows the W-TiO2 nanostructured photocatalyst sample's exceptional photocatalytic performance. The band gap energies of TiO2 and W-TiO2 were determined through optical studies to be 3.22 eV and 2.93 eV, respectively, showing an improvement in the photocatalytic activity of TiO2 in the visible light domain. Studies of the photocatalytic performance indicated that the full treatment of MX-5B molecules was achieved after 105, 100, 95, 80, 70, 85, and 90 min of exposure to visible light for pure TiO2, W0.5-TiO2, W1-TiO2, W3-TiO2, W5-TiO2, W8-TiO2, and W10-TiO2, respectively. These studies revealed the great and quick photocatalytic treatment of MX-5B in the presence of doped TiO2. The results of a study that used 400 mL of a 40 mg/L MX-5B solution prepared with deionized water as a control sample and a sample of actual textile wastewater as a real sample showed that MX-5B from actual textile wastewater was effectively photocatalytically degraded in the presence of W5-TiO2 photocatalyst.

Increase and enrichment of active electrons by carbon dots induced to improve TiO2 photocatalytic hydrogen production activity

Recombination of photogenerated carriers severely reduces the efficiency of photocatalytic reactions. Herein, Bio-CDs/TiO2 were produced using the hydrothermal method to tightly load biomass-based carbon dots (Bio-CDs) onto the surface of TiO2via Ti-O-C bonds. Finite-difference time-domain (FDTD) simulations showed that the Bio-CDs act as electron storage pools in the Bio-CDs/TiO2, enhancing optical absorption and promoting the transfer and storage of photogenerated electrons from TiO2 to the Bio-CDs, and thus effectively inhibiting the recombination of electron-hole pairs. Photocatalytic hydrogen production by the Bio-CDs/TiO2 was significantly improved compared with that by pristine TiO2 (603.92 μmol h−1 g−1vs 94.18 μmol h−1 g−1) and, importantly, the Bio-CDs/TiO2 performed well over several cycles. Surprisingly, Bio-CDs/TiO2 also exhibits nice catalytic performance for hydrogen production under the combined action of photoelectricity, and its Tafel slope was significantly lower than that of pristine TiO2, which confirmed that the same research potential of Bio-CDs/TiO2 in the field of photoelectrocatalysis. This work introduces new ways to study the synergistic effects of multiple mechanisms (enhanced optical absorption, increased separation of photogenerated carriers and promotion of transfer and storage of photogenerated electrons) in the enhancement of photocatalytic and photoelectrocatalytic activity of semiconductors by carbon dots.

Removal of Carbamazepine in Aqueous Solution by TiO2 Ceramic Photo-Catalyst under Simulated Solar Light: Kinetics, Effects of Environmental Factors and Degradation Pathways

Current research on the photocatalytic activity of TiO2 mainly focuses on its nano- or micro-particle forms, which are difficult to recycle and apply in real engineering applications. This study aims to apply a small pilot of TiO2 in the ceramic form to remove carbamazepine (CBZ) from an aqueous solution under simulated sunlight. A high removal efficiency up to >99% was shown in a 5 mg L−1 CBZ solution after 6 h of irradiation with a total energy of 150.92 kJ. The kinetic degradation was not affected in an alkaline solution (at pH 7, pH 10, and pH 13) but was faster under acidic conditions (pH 2) in which CBZ existed in the protonated form. The presence of NO3− (10–50 mg L−1) slightly affected the photodegradation of CBZ while humic acid significantly reduced the photocatalytic activity. In addition, the presence of major ions in water also had a negative effect at concentrations between 10 and 50 mg L−1. The MS/MS was used to identify the transformation products of CBZ, and a possible degradation mechanism was proposed. The toxicity of CBZ and the by-products was primarily evaluated. The results showed that TiO2 ceramics show high reusability and stability with a photocatalytic performance of >95% and a mass loss of <5% after 90 degradation cycles.

Mechanically robust, thermally insulating and photo-responsive aerogels designed from sol-gel electrospun PVP-TiO2 nanofibers

We present a robust approach for fabricating polyvinylpyrrolidone (PVP)-titania (TiO2) nanofibrous aerogels (NFA) with multifunctional and triggered performances. These low density (∼ 10 mg cm−3) 3D self-supported aerogels having an intrinsically lamellar porous structure (> 99% porosity) are created via solid templating of sol-gel electrospun PVP-TiO2 hybrid nanofibers. The photocatalytic activity of TiO2 allows for on-demand application wherein the aerogel exhibits antibacterial properties upon UV exposure to bacteria such as Escherichia coli and Salmonella enterica. Significantly, while the aerogel sorbs common volatile organic components (VOCs) or oil due to its innate porosity, exposure of the aerogel to ultraviolet (UV) radiation leads to their decomposition. The PVP-TiO2 NFA exhibits a low thermal conductivity (0.062 W m−1K−1) together with considerable mechanical flexibility up to strains of 50% with >90% recovery, without the need for post-processing. The photo-responsive attributes combined with mechanical resilience, oleophilicity and thermal insulation properties render these aerogels viable candidates for a diverse range of applications. We discuss such property enhancements in terms of the interaction between PVP and TiO2 and aerogel microstructure.

Polymer Membrane Modified with Photocatalytic and Plasmonic Nanoparticles for Self-Cleaning Filters.

In this study, we developed a filtering material for facial masks, which is capable of trapping and subsequent inactivation of bacteria under white light emitting diodes (LED) or sunlight irradiation. Such a functionality is achieved via the modification of the composite membrane based on porous polymer with photocatalytic (TiO2) and plasmonic (Ag) nanoparticles. The porous polymer is produced by means of a computer numerical control machine, which rolls a photoresist/thermoplastic mixture into a ~20-µm-thick membrane followed by its thermal/ultraviolet (UV) hardening and porosification. TiO2 nanoparticles are prepared by hydrothermal and sol-gel techniques. Colloidal synthesis is utilized to fabricate Ag nanoparticles. The TiO2 photocatalytic activity under UV excitation as well as a photothermal effect generated by plasmonic Ag nanoparticles subjected to LED irradiation are studied by the assessment of methylene blue (MB) decomposition. We demonstrate that, in contrast to the filter of the standard facial medical mask, the polymer membrane modified with spray-coated TiO2 and Ag nanoparticles prevents the penetration of bacillus subtilis from its top to bottom side and significantly inhibits bacterial growth when exposed to LED or sunlight.

The impact of Carbon Quantum Dots (CQDs) on the photocatalytic activity of TiO2 under UV and visible light

In this study, the impact of carbon quantum dots (CQDs) on the photocatalytic performance of TiO2 in aqueous medium was investigated under UV and visible light. CQDs were synthesized through a solvothermal procedure, and the effect of synthesis conditions on their optical properties were optimized. The CQDs/TiO2 nanocomposites were prepared via a hydrothermal method using CQDs with the extreme band-gaps (i.e. CQDs450 and CQDs550). The physicochemical properties of CQDs and CQDs/TiO2 samples were studied by various characterization techniques. According to the High-Resolution Tunneling Electron microscopy (HRTEM) micrographs, the synthesized spherical CQDs had diameters smaller than 5 nm. The Diffuse Reflectance Spectroscopy (DRS) analysis revealed that incorporation of CQDs into nanocomposite samples causes a remarkable shift in absorption edge to the visible region, in comparison with pure TiO2. According to the experimental data, the nanocomposite sample containing CQDs with the higher absorption edge, i.e. CQDs550/TiO2, showed a superior performance in photocatalytic removal of methylene blue (MB) under visible light. In this regard, the removal percent of MB on CQDs550/TiO2 and CQDs450/TiO2 nanocomposites, with 4%wt CQDs, under visible light (λ > 420 nm) were 92.1 % and 53.4 % after 120 min of irradiation at pH = 11 and 150 mgcat./L catalyst dosage, which are respectively 2.4 and 1.4 times higher than that on pure TiO2. However, under UV irradiation the observed photocatalytic performances were in the reverse order. Finally, two different reaction mechanisms have been proposed to explain the obtained results on CQDs/TiO2 samples, based on possible electron transfer between TiO2 and CQDs nanoparticles under UV and Visible lights.