Facile Preparation and Lithium Storage Properties of TiO2@Graphene Composite Electrodes with Low Carbon Content

Over the past decade, TiO₂/graphene composites as electrodes for lithium ion batteries have attracted a great deal of attention for reasons of safety and environmental friendliness. However, most of the TiO₂/graphene electrodes have large graphene content (9–40 %), which is bound to increase the cost of the battery. Logically, reducing the amount of graphene is a necessary part to achieve a green battery. The synthesis of TiO₂ nanosheets under solvothermal conditions without additives is now demonstrated. Through mechanical mixing TiO₂ nanosheets with different amount of reduced graphene (rGO), a series of TiO₂@graphene composites was prepared with low graphene content (rGO content 1, 2, 3, and 5 wt %). When these composites were evaluated as anodes for lithium ion batteries, it was found that TiO₂+3 wt % rGO manifested excellent cycling stability and a high specific capacity (243.7 mAh g^?1 at 1 C; 1 C=167.5 mA g^?1), and demonstrated superior high‐rate discharge/charge capability at 20 C.     

Single-step solvothermal synthesis of mesoporous anatase TiO<Subscript>2</Subscript>-reduced graphene oxide nanocomposites for the abatement of organic pollutants

In the present work, we have fabricated a novel mesoporous TiO₂–rGO nanocomposite by a facile one-step solvothermal method using titanic sulfate as the TiO₂ source. The as-prepared composites were characterized by transmission electron microscopy, X-ray diffraction; UV–Vis diffuse reflectance spectra, X-ray photoelectron spectroscopy and photoluminence spectra. In situ nucleation and anchoring of TiO₂ nanoparticles onto a graphene sheet is favorable fpr forming an intimate interfacial contact, and the chemically bonded TiO₂–rGO nanocomposites commendably enhanced their photocatalytic activity in the photodegradation of rhodamine B and phenol. The high photocatalytic activity of the as-synthesized nanocomposites are primarily ascribed to the mesoporous structure, efficient charge transportation and separation with enhanced visible light absorption, which come from the appealing nanoarchitecture, for instance, ultra-dispersed and ultra-small TiO₂ nanocrystals along with intimate and absolute interfacial contact between the TiO₂ nanocrystals and the graphene sheet.     

Doping of TiO2–GO and TiO2–rGO with Noble Metals: Synthesis,Characterization and Photocatalytic Performance for Azo Dye Discoloration

The nanocomposites of titania coupled with graphene oxide (GO) and reduced graphene oxide (rGO), respectively, were prepared by homogeneous hydrolysis with urea. Graphene was obtained by effect of high‐intensity cavitation field on natural graphite in the presence of strong aprotic solvents in pressurized ultrasonic reactor. The morphology of TiO₂–GO and TiO₂–rGO composites was assessed by scanning electron microscopy and atomic force microscopy. The nitrogen adsorption–desorption was used for determination of surface area (BET) and porosity. Raman and IR spectroscopy were used for qualitative analysis and diffuse reflectance spectroscopy was employed to estimate band‐gap energies. Further enhancement of the photocatalytic activity was attained by codoping of composites with noble metals—Au, Pd and Pt. The photocatalytic activity of TiO₂–GO and TiO₂–rGO were assessed by photocatalytic decomposition of Orange II dye in an aqueous slurry under UV and visible light irradiation. The photocatalytic activity of noble metals codoped samples was determined with decomposition of Reactive Black 5 azo dye.     

Photocatalytic activity of polyaniline/Fe-doped TiO2 composites by in situ polymerization method

This study was focused on the photocatalytic activity of polyaniline (Pani)/iron doped titanium dioxide (Fe–TiO₂) composites for the degradation of methylene blue as a model dye. TiO₂ nanoparticles were doped with iron ions (Fe) using the wet impregnation method and the doped nanoparticles were further combined with Pani via an in situ polymerization method. For comparison purposes, Pani composites were also synthesized in the presence undoped TiO₂. The photocatalyst and the composites were characterized by standard analytical techniques such as FTIR, XRD, SEM, EDX and UV–Vis spectroscopies. Fe–TiO₂ and its composites exhibited enhanced photocatalytic activity under ultraviolet light irradiation. Improved photocatalytic activity of Fe–TiO₂ was attributed to the dopant Fe ions hindering the recombination of the photoinduced charge carriers. Pani/Fe–TiO₂ composite with 30?wt.% of TiO₂ nanoparticles achieved 28% dye removal and the discoloration rate of methylene blue for the sample was 0.0025?min^?1. FTIR, XRD, SEM, EDX and UV–Vis spectroscopies supported the idea that Fe ions integrated into TiO₂ crystal structure and Pani composites were successfully synthesized in the presence of the photocatalyst nanoparticles. The novelty of this study was to investigate the photocatalytic activity of Pani composites, containing iron doped TiO₂ and to compare their results with that of Pani/TiO₂.     

Azo dyes degradation using TiO2-Pt/graphene oxide and TiO2-Pt/reduced graphene oxide photocatalysts under UV and natural sunlight irradiation

The photocatalytic degradation of azo dyes with different structures (amaranth, sunset yellow and tartrazine) using TiO₂-Pt nanoparticles (TPt), TiO₂-Pt/graphene oxide (TPt-GO) and TiO₂-Pt/reduced graphene oxide (TPt-rGO) composites were investigated in the presence of UV and natural sunlight irradiation. The composites were prepared by a combined chemical-thermal method and characterized by Transmission Electron Microscopy (TEM), X-ray powder diffraction (XRD), Infrared (FTIR) and UV–Vis spectroscopy. The modification of TiO₂-Pt with graphene oxide shifted its optical absorption edge towards the visible region and increased its photocatalytic activity under UV and natural sunlight irradiation. The efficiency of catalysts on azo dyes degradation (in similar conditions) reached high values (above 99%) under sunlight conditions, proving the remarkable photocatalytic activities of obtained composites. TPt-GO nanocomposite exhibited higher photoactivity than TPt or TPt-rGO, demonstrating degradation efficiencies of 99.56% for amaranth, 99.15% for sunset yellow and 96.23% for tartrazine. The dye photodegradation process follows a pseudo-first-order kinetic with respect to the Langmuir-Hinshelwood reaction mechanism. A direct dependence between azo dyes degradation rate and chemical structure of dyes has been observed.     

Optimal TiO2–Graphene Oxide Nanocomposite for Photocatalytic Activity under Sunlight Condition: Synthesis,Characterization, and Kinetics

TiO₂–graphene oxide nanocomposites have been fabricated by the sol–gel technique for degradation of a typical cationic dye solution. The prepared photocatalysts were characterized by X‐ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric‐differential analyses, Brunauer–Emmett–Teller surface area measurement, and scanning and transmission electron microscopy. In addition, the photocatalytic activities of samples were evaluated by degradation of methylene blue aqueous solution under the sunlight irradiation. The change in color of solution was evaluated by the UV–vis spectroscopy, and the maximum photocatalytic decoloration (94%) was achieved within 60 min, which exceeded that of pure anatase under the same conditions. The results show that the nanocomposite containing 9.0 wt% of graphene oxide has the superior photocatalytic performance to either single‐phase anatase or other composites containing different amounts of graphene oxide. The experimental degradation data obtained from the batch tests were analyzed by a modified kinetic model, which predicted the performance with higher regression coefficients and lower relative errors. The distribution of TiO₂ nanoparticles (<20 nm) on graphene oxide sheets is proposed to be the efficient factor in the homogeneous degradation of dye which can concomitantly improve the photocatalytic activity.     

Nanostructured Graphene/TiO2 Hybrids as High‐Performance Anodes for Microbial Fuel Cells

A new nanostructured graphene/TiO₂ (G/TiO₂) hybrid was synthesized by a facile microwave‐assisted solvothermal process in which amorphous TiO₂ was assembled on graphene in situ. The resulting G/TiO₂ hybrids were characterized by XRD, SEM, TEM, Raman spectroscopy, and N₂ adsorption/desorption analysis. The electrochemical properties of the hybrids as anode materials for Shewanella‐inoculated microbial fuel cells (MFCs) were studied for the first time, and they proved to be effective in improving MFC performance. The significantly improved bacterial attachment and extracellular electron‐transfer efficiency could be attributed to the high specific surface area, active groups, large pore volume, and excellent conductivity of the nanostructured G/TiO₂ hybrid, and this suggests that it could be a promising candidate for high‐performance MFCs.     

Synthesis,characterization and photocatalytic application of TiO2/magnetic graphene for efficient photodegradation of crystal violet

A magnetized nano‐photocatalyst based on TiO₂/magnetic graphene was developed for efficient photodegradation of crystal violet (CV). Scanning electron microscopy, X‐ray diffraction, energy‐dispersive X‐ray spectroscopy and elemental mapping were used to characterize the prepared magnetic nano‐photocatalyst. The photocatalytic activity of the synthesized magnetic nano‐photocatalyst was evaluated using the decomposition of CV as a model organic pollutant under UV light irradiation. The obtained results showed that TiO₂/magnetic graphene exhibited much higher photocatalytic performance than bare TiO₂. Incorporation of graphene enhanced the activity of the prepared magnetic nano‐photocatalyst. TiO₂/magnetic graphene can be easily separated from an aqueous solution by applying an external magnetic field. Effects of pH, magnetized nano‐photocatalyst dosage, UV light irradiation time, H₂O₂ amount and initial concentration of dye on the photodegradation efficiency were evaluated and optimized. Efficient photodegradation (>98%) of the selected dye under optimized conditions using the synthesized nano‐photocatalyst under UV light irradiation was achieved in 25 min. The prepared magnetic nano‐photocatalyst can be used in a wide pH range (4–10) for degradation of CV. The effects of scavengers, namely methanol (OH^? scavenger), p‐benzoquinone (O₂^?? scavenger) and disodium ethylenediaminetetraacetate (hole scavenger), on CV photodegradation were investigated.     

Template‐Free Synthesis of Core–Shell TiO2 Microspheres Covered with High‐Energy {116}‐Facet‐Exposed N‐Doped Nanosheets and Enhanced Photocatalytic Activity under Visible Light

Core–shell TiO₂ microspheres possess a unique structure and interesting properties, and therefore, they have received much attention. The high‐energy facets of TiO₂ also are being widely studied for the high photocatalytic activities they are associated with. However, the synthesis of the core–shell structure is difficult to achieve and requires multiple‐steps and/or is expensive. Hydrofluoric acid (HF), which is highly corrosive, is usually used in the controlling high‐energy facet production. Therefore, it is still a significant challenge to develop low‐temperature, template‐free, shape‐controlled, and relative green self‐assembly routes for the formation of core–shell‐structured TiO₂ microspheres with high‐energy facets. Here, we report a template‐ and hydrofluoric acid free solvothermal self‐assembly approach to synthesize core–shell TiO₂ microspheres covered with high‐energy {116}‐facet‐exposed nanosheets, an approach in which 1,4‐butanediamine plays a key role in the formation of nanosheets with exposed {116} facets and the doping of nitrogen in situ. In the structure, nanoparticle aggregates and nanosheets with {116} high‐energy facets exposed act as core and shell, respectively. The photocatalytic activity for degradation of 2,4,6‐tribromophenol and Rhodamine B under visible irradiation and UV/Vis irradiation has been examined, and improved photocatalytic activity under visible light owing to the hierarchical core–shell structure, {116}‐plane‐oriented nanosheets, in situ N doping, and large surface areas has been found.     

Solvothermal synthesis of WO3/TiO2/carbon fiber composite photocatalysts for enhanced performance under sunlight illumination

Carbon fiber (CF)‐based WO₃/TiO₂ composite catalysts (WO₃/TiO₂/CF) were successfully synthesized by solvothermal method. The catalysts were characterized by XPS, SEM, BET, XRD, FTIR, Raman and UV–Vis. The analyses confirmed the WO₃/TiO₂ nanoparticles with high crystallinity deposited on the carbon structure. The photocatalytic degradation of Orange II azo dye under UV and sunlight illumination with the synthesized catalyst was explored. The composite catalyst displayed high performance (85%) for Orange II degradation while that of for WO₃/TiO₂ was found as 76%. The effects of CF amount, solution pH, initial dye concentration and catalyst dose on photocatalytic performance were studied. It was found that the degradation efficiency increased from 68% to 90% with the increasing CF amount from 3 wt% to 5 wt%, while the further increase in CF amount (7–10 wt%) decreased the photodegradation due to the blocking the active sites of WO₃/TiO₂. The enhanced photocatalytic efficiency was mainly attributed to the electrical properties of the CF and reduced bandgap.     

Synthesis and Study of Plasmon‐Induced Carrier Behavior at Ag/TiO2 Nanowires

Nanocomposites of Ag/TiO₂ nanowires with enhanced photoelectrochemical performance have been prepared by a facile solvothermal synthesis of TiO₂ nanowires and subsequent photoreduction of Ag⁺ ions to Ag nanoparticles (AgNPs) on the TiO₂ nanowires. The as‐prepared nanocomposites exhibited significantly improved cathodic photocurrent responses under visible‐light illumination, which is attributed to the local electric field enhancement of plasmon resonance effect near the TiO₂ surface rather than by the direct transfer of charge between the two materials. The visible‐light‐driven photocatalytic performance of these nanocomposites in the degradation of methylene blue dye was also studied, and the observed improvement in photocatalytic activity is associated with the extended light absorption range and efficient charge separation due to surface plasmon resonance effect of AgNPs.     

Efficient CO2 Capture and Photoreduction by Amine‐Functionalized TiO2

Amine‐functionalization of TiO₂ nanoparticles, through a solvothermal approach, substantially increases the affinity of CO₂ on TiO₂ surfaces through chemisorption. This chemisorption allows for more effective activation of CO₂ and charge transfer from excited TiO₂, and significantly enhances the photocatalytic rate of CO₂ reduction into methane and CO.     

Template‐free Fabrication of Hierarchical Macro‐/mesoporous N‐doped TiO2/graphene Oxide Composites with Enhanced Visible‐light Photocatalytic Activity

Hierarchical macro‐/mesoporous N‐doped TiO₂/graphene oxide (N‐TiO₂/GO) composites were prepared without using templates by the simple dropwise addition mixed solution of tetrabutyl titanate and ethanol containg graphene oxide (GO) to the ammonia solution, and then calcined at 350 °C. The as‐prepared samples were characterized by scanning electron microscopy (SEM), Brunauer‐Emmett‐Teller (BET) surface area, X‐ray diffraction (XRD), Raman spectroscopy, X‐ray photoelectron spectroscopy (XPS), and UV‐Vis absorption spectroscopy. The photocatalytic activity was evaluated by the photocatalytic degradation of methyl orange in an aqueous solution under visible‐light irradiation. The results show that N‐TiO₂/GO composites exhibited enhanced photocatalytic activity. GO content exhibited an obvious influence on photocatalytic performance, and the optimal GO addition content was 1 wt%. The enhanced photocatalytic activity could be attributed to the synergetic effects of three factors including the improved visible light absorption, the hierarchical macro‐mesoporous structure, and the efficient charge separation by GO.     

Facile decoration of TiO2 nanoparticles on graphene for solar degradation of organic dye

The reduced graphene oxide is interesting material for the synthesis of TiO₂-based photocatalyst. In the present investigation, blackberry fruit, which contains high levels of anthocyanins and other phenolic compounds, was employed as a reducing agent mainly due to its high antioxidant capacity. The nano-crystalline TiO₂ was decorated on different amounts of graphene oxide with sol–gel method and then the photocatalytic activity for degradation of cationic dye was evaluated by UV spectroscopy to achieve the optimum content of graphene oxide. The decoration of anatase nanoparticles on prepared reduced graphene oxide was investigated by X-ray diffraction, scanning and transmission electron microscopy techniques. The new composite gives significantly higher activity when is compared to the compositions fabricated by graphene oxide. The compact layer provides a large TiO₂-graphene contact area and reduces the electron recombination. The decoration of TiO₂ nanoparticles, 5–10 nm, on the graphene oxide reduced by blackberry juice further improves the dye removal. The results imply that the nanoparticle decoration is the key strategy to increase the degradation capacity.     

Understanding the Electronic Structures of Graphene Quantum Dot Physisorption and Chemisorption onto the TiO2 (110) Surface: A First‐Principles Calculation

We investigated the interfacial electronic structure and charge transfer properties of graphene quantum dot (GQD) physisorption and chemisorption on the TiO₂ (110) surface from density functional theory calculations. The simulations show that a slight charge transfer occurs in physisorption case while a significant charge transfer takes place in chemisorption configuration. We present a detailed comparison of the similarities and differences between the electronic structures. The similarities originate from the positive work function difference in both the physisorption and chemisorption configurations, which is able to drive electron transfer from GQD into TiO₂, leading to charge separation across the GQD–TiO₂ interface. The differences stem from the interaction between the GQD and TiO₂ substrate. For example, GQD bounds to TiO₂ surface through van der Waals interactions in the case of physisorption. In the chemisorption configuration, however, there exists strong covalent bonding between them. This leads to much more efficient charge separation for chemisorption than for physisorption. Furthermore, the GQD–TiO₂ composites show large band‐gap narrowing that could extend the optical absorption edge into the visible‐light region. This should imply that chemisorbed GQDs produce a composite with better photocatalytic and photovoltaic performance than composites formed through physisorption.     

Improved Photodegradation of Organic Contaminants Using Nano‐TiO2 and TiO2–SiO2 Deposited on Portland Cement Concrete Blocks

The photocatalytic activity of TiO₂ nanoparticles (nano‐TiO₂) and its hybrid with SiO₂ (nano‐TiO₂–SiO₂) for degradation of some organic dyes on cementitious materials was studied in this work. Nanohybrid photocatalysts were prepared using an inorganic sol–gel precursor and then characterized using XRD, SEM and UV–Vis. The grain sizes were estimated by Scherrer's equation to be around 10 nm. Then, a thin layer was applied to Portland cement concrete (PCC) blocks by dipping them into nano‐TiO₂ and nano‐TiO₂–SiO₂ solution. The efficiency of coated PCC blocks for the photocatalytic decomposition of two dyes, Malachite Green oxalate (MG) and Methylene Blue (MB), was examined under UV and visible irradiation and then monitored by the chemical oxygen demand tests. The results showed that more than 80% and 92% of MG and MB were decomposed under UV–Vis irradiation using blocks coated with nano‐TiO₂–SiO₂. TiO₂/PCC and TiO₂–SiO₂/PCC blocks showed a significant ability to oxidize dyes under visible and UV lights and TiO₂–SiO₂/PCC blocks require less time for dye degradation. Based on these results, coated blocks have increased photocatalytic activity which can make them commercially accessible photocatalysts.     

Enhanced Photocatalytic Hydrogen‐Production Performance of Graphene–ZnxCd1−xS Composites by Using an Organic S Source

In response to the increasing concerns over energy and environmental sustainability, photocatalytic water‐splitting technology has attracted broad attention for its application in directly converting solar energy to valuable hydrogen (H₂) energy. In this study, high‐efficiency visible‐light‐driven photocatalytic H₂ production without the assistance of precious‐metal cocatalysts was achieved on graphene–Zn_xCd_1?xS composites with controlled compositions. The graphene‐Zn_xCd_1?xS composites were for the first time fabricated by a one‐step hydrothermal method with thiourea as an organic S source. It was found that thiourea facilitates heterogeneous nucleation of Zn_xCd_1?xS and in situ growth of Zn_xCd_1?xS nanoparticles on graphene nanosheets. Such a scenario results in abundant and intimate interfacial contact between graphene and Zn_xCd_1?xS nanoparticles, efficient transfer of the photogenerated charge carriers, and enhanced photocatalytic activity for H₂ production. The highest H₂‐production rate of 1.06 mmol h^?1 g^?1 was achieved on a graphene–Zn_0.5Cd_0.5S composite photocatalyst with a graphene content of 0.5 wt %, and the apparent quantum efficiency was 19.8 % at 420 nm. In comparison, the graphene–Zn_xCd_1?xS composite photocatalyst prepared by using an inorganic S source such as Na₂S exhibited much lower activity for photocatalytic H₂ production. In this case, homogeneous nucleation of Zn_xCd_1?xS becomes predominant and results in insufficient and loose contact with the graphene backbone through weak van der Waals forces and a large particle size. This study highlights the significance of the choice of S source in the design and fabrication of advanced graphene‐based sulfide photocatalytic materials with enhanced activity for photocatalytic H₂ production.     

溶剂热法制备Ag/TiO_2纳米材料及其光催化性能

以乙醇为溶剂,钛酸四丁酯为前驱体,用溶剂热法制备了Ag表面修饰的负载型纳米二氧化钛光催化剂.利用X射线衍射(XRD)、N2吸附-脱附(BET)、透射电子显微镜(TEM)、X射线光电子能谱(XPS)、紫外-可见(UV-Vis)光谱等技术对其进行了系统的表征,以亚甲基蓝(MB)溶液的脱色降解为模型反应,考察了不同Ag含量样品的光催化性能.结果表明:用溶剂热法制备的样品中TiO2皆为锐钛矿相,金属Ag颗粒沉积在TiO2表面,粒径为2nm左右,比表面积较溶胶凝胶法制备的样品大大增加,最高可达151.44m2·g-1;UV-Vis光谱和光催化实验表明:Ag修饰使TiO2对光的吸收能力大大增强,吸收带边红移至可见光区,亚甲基蓝在该复合材料上的光催化降解反应遵循一级反应动力学模型;溶剂热法制备样品的光催化性能明显好于溶胶凝胶法制备的样品,在紫外光和可见光下,Ag摩尔分数为5%的样品表现出最佳的光催化活性.     

Graphene Nanosheets as a Platform for the 2D Ordering of Metal Oxide Nanoparticles: Mesoporous 2D Aggregate of Anatase TiO2 Nanoparticles with Improved Electrode Performance

Graphene nanosheets are successfully applied as an effective platform for the 2D ordering of metal oxide nanoparticles. Mesoporous 2D aggregates of anatase TiO₂ nanoparticles are synthesized by the heat treatment of the uniformly hybridized nanocomposite of layered titanate–reduced graphene oxide (RGO) at elevated temperatures. The precursor layered titanate–RGO nanocomposite is prepared by self‐assembly of anionic RGO nanosheets and cationic TiO₂ nanosols. The calcination of the as‐prepared layered titanate–RGO nanocomposite at 500 °C induces a structural and morphological change of layered titanate nanoplates into anatase TiO₂ nanoparticles without significant modification of the RGO nanosheet. Increasing the heating temperature to 600 °C gives rise to elimination of the RGO component, leading to the formation of sheetlike porous aggregates of RGO‐free TiO₂ nanoparticles. The nanocomposites calcined at 500–700 °C display promising functionality as negative electrodes for lithium ion batteries. Among the present calcined derivatives, the 2D sheet‐shaped aggregate of TiO₂ nanoparticles obtained from calcination at 600 °C delivers the greatest specific discharge capacity with good capacity retention for all current density conditions applied. Such superior electrode performance of the nanocomposite calcined at 600 °C is attributable both to the improved stability of the crystal structure and crystal morphology of titania and to the enhancement of Li⁺ ion transport through the enlargement of mesopores. The present findings clearly demonstrate the usefulness of RGO nanosheets as a platform for 2D‐ordered superstructures of metal oxide nanoparticles with improved electrode performance.     

In‐tube solid‐phase microextraction capillary column packed with mesoporous TiO2 nanoparticles for phosphopeptide analysis

In this study, an in‐tube solid‐phase microextraction column packed with mesoporous TiO₂ nanoparticles, coupled with MALDI–TOF–MS, was applied to the selective enrichment and detection of phosphopeptides in complex biological samples. The mesoporous TiO₂ nanoparticles with high specific surface areas, prepared by a sol–gel and solvothermal method, were injected into the capillary using a slurry packing method with in situ polymerized monolithic segments as frits. Compared with the traditional solid‐phase extraction method, the TiO₂‐packed column with an effective length of 1 cm exhibited excellent selectivity (α‐casein/β‐casein/BSA molar ratio of 1:1:100) and sensitivity (10 fmol of a β‐casein enzymatic hydrolysis sample) for the enrichment of phosphopeptides. These performance characteristics make this system suitable for the detection of phosphorylated peptides in practical biosamples, such as nonfat milk.