TiO2 Heterojunction Photocatalysts Research Articles

Photocatalytic degradation of sulfamethazine using g-C3N4/TiO2 heterojunction photocatalyst: Performance, mechanism insight and degradation pathway

In the present research, Z-scheme g-C3N4/TiO2 heterojunction composite photocatalysts with varied g-C3N4 content were successfully prepared using the sol-gel technique combined with calcination methods. The morphology, crystallinity, chemical composition, and optical properties of the synthesized catalysts were characterized employing a series of techniques. Sulfamethazine (SMZ) was selected as the model pollutant to evaluate the photocatalytic activity of the prepared catalysts employing a 500 W xenon lamp as the light source to simulate sunlight. The results demonstrated that within 180 min of irradiation, 94.8 % of SMZ was removed by using the optimal photocatalyst (0.4CN/TiO2 composite sample), affording an apparent first-order rate coefficient of 0.0152 min−1 which was 3.8 or 2.0 times as much as that involving single g-C3N4 or TiO2 catalyst, respectively. The effects of catalyst dosage, initial pH, different water matrices, different substrates, and inorganic ions on the performance of 0.4CN/TiO2 photocatalyst were explored. Furthermore, the 0.4CN/TiO2 composite also displayed satisfactory cyclic stability. The results of radical quenching experiments revealed that the key active species in SMZ degradation were hydroxyl radicals (•OH), superoxide radicals (O2•−), and holes (h+). The efficient separation of photo-generated electrons and holes originating in the formation of a Z-scheme g-C3N4/TiO2 heterojunction was evidenced by photoluminescence and electrochemical impedance spectroscopy determination and should be responsible for the enhanced catalytic activity of the 0.4CN/TiO2 sample. In addition, the plausible pathways for the aqueous degradation of SMZ were suggested according to the identified degradation intermediates employing the HPLC/MS technique. In summary, the current research provides a novel insight into the development of Z-scheme heterojunctions in the realm of organic pollutant treatment.

Synthesis of AgCl/ZIF-8/C–TiO2 heterojunction photocatalysts for enhanced degradation of levofloxacin under visible-light

The design of photocatalytic heterojunctions for the degradation of organic contaminants from wastewater under visible illumination has attracted much attention recently. Through these heterojunctions, the separation efficiency of photogenerated charges can be increased, thus enhancing photocatalytic activity. Herein, ternary heterojunctions composed of carbon-doped TiO2 (C–TiO2) decorated by Zn-zeolitic imidazole framework (ZIF-8) and AgCl have been constructed as photocatalysts by facile deposition and precipitation routes with the aim of degrading organic pollutants in water (levofloxacin (LVFX) antibiotic). The developed heterojunction structure of C–TiO2, ZIF-8, and AgCl synergistically contributed to the efficient transfer of photo-charges and prevention of their recombination, thus achieving high photocatalytic efficiency, in which 98 % of LVFX can be decomposed within 60 min under solar illumination. The outstanding performance of the AgCl/ZIF-8/C–TiO2 composite was credited to the dual heterojunctions of AgCl and C–TiO2 with ZIF-8, which decreased the degree of photogenerated carrier's recombination. Accordingly, the proposed mechanism and the photodegradation pathways have been detailedly elucidated. Also, it was confirmed through trapping experiments that •O2- and h+ were considered the most effective species in the photodegradation process. Moreover, the AgCl/ZIF-8/C–TiO2 photocatalyst system displayed remarkable photostability during successive photocatalysis.

Self‐sacrificial Templated Synthesis of Fe/N Co‐doping TiO2 for Enhanced CO2 Photocatalytic Reduction

AbstractAs a green photocatalyst, TiO2 has been widely used in adsorption, desorption and redox reactions, but the wide energy band and moderate visible light absorption have greatly inhibited its applications in photocatalysis. The effective method of enhancing the performance of catalysts is the development of heterojunction and metal‐nonmetal co‐doping. Herein, Fe−N co‐doped TiO2 heterojunction photocatalysts (FexTi@C) were successfully synthesized by calcining a self‐sacrificial template (NH2−MIL‐125(Ti)) injected with Fe3+ solution. X‐ray diffraction (XRD), transmission electron microscopy (TEM), X‐ray photoelectron spectroscopy (XPS), N2 adsorption/desorption analysis, and photoelectrochemical tests were used to characterize FexTi@C, showing multiple rutile/anatase TiO2 heterojunction structure, low bandgap, and significant absorption in visible light. In addition, the Ti−O−Fe tetrahedra and more oxygen vacancies were provided since the doped N is from the pristine MOF and the radii of Fe3+ and Ti4+ are similar, which improved the photocatalytic efficiency of CO2 reduction to CH4, especially the Fe0.8Ti@C reached 7.8‐fold and 10.2‐fold CH4 yield increase compared with the original TiMOF template and the undoped Ti@C, respectively. This work presents a simple method for the fabrication of low bandgap semiconductors, and also makes a new attempt at the synergistic effect between the in‐situ elements and valence bonds of MOF‐derived catalysts.

Oxygen Vacancy Mediated Band-Gap Engineering via B-Doping for Enhancing Z-Scheme A-TiO2/R-TiO2 Heterojunction Photocatalytic Performance.

Fabrication of Z-scheme heterojunction photocatalysts is an ideal strategy for solving environmental problems by providing inexhaustible solar energy. A direct Z-scheme anatase TiO2/rutile TiO2 heterojunction photocatalyst was prepared using a facile B-doping strategy. The band structure and oxygen-vacancy content can be successfully tailored by controlling the amount of B-dopant. The photocatalytic performance was enhanced via the Z-scheme transfer path formed between the B doped anatase-TiO2 and rutile-TiO2, optimized band structure with markedly positively shifted band potentials, and the synergistically-mediated oxygen vacancy contents. Moreover, the optimization study indicated that 10% B-doping with the R-TiO2 to A-TiO2 weight ratio of 0.04 could achieve the highest photocatalytic performance. This work may provide an effective approach to synthesize nonmetal-doped semiconductor photocatalysts with tunable-energy structures and promote the efficiency of charge separation.

Recent Advances in Black TiO2 Nanomaterials for Solar Energy Conversion.

Titanium dioxide (TiO2) nanomaterials have been widely used in photocatalytic energy conversion and environmental remediation due to their advantages of low cost, chemical stability, and relatively high photo-activity. However, applications of TiO2 have been restricted in the ultraviolet range because of the wide band gap. Broadening the light absorption of TiO2 nanomaterials is an efficient way to improve the photocatalytic activity. Thus, black TiO2 with extended light response range in the visible light and even near infrared light has been extensively exploited as efficient photocatalysts in the last decade. This review represents an attempt to conclude the recent developments in black TiO2 nanomaterials synthesized by modified treatment, which presented different structure, morphological features, reduced band gap, and enhanced solar energy harvesting efficiency. Special emphasis has been given to the newly developed synthetic methods, porous black TiO2, and the approaches for further improving the photocatalytic activity of black TiO2. Various black TiO2, doped black TiO2, metal-loaded black TiO2 and black TiO2 heterojunction photocatalysts, and their photocatalytic applications and mechanisms in the field of energy and environment are summarized in this review, to provide useful insights and new ideas in the related field.

Synthesis and Characterization of BaTiO3/TiO2 Heterojunction Photocatalyst for Novel Application in Photocatalytic Degradation of TBBPA under Simulated Sunlight Irradiation

AbstractThe polyacrylamide gel method combined with low temperature sintering technology (PGMCLTST) have been used to synthesize the BaTiO3/TiO2 heterojunction photocatalysts. The BaTiO3/TiO2 heterojunction photocatalyst only contains tetragonal BaTiO3, rutile TiO2 and anatase TiO2, without any other impurities. Based on a variety of characterization, it was confirmed that a special heterojunction was formed between BaTiO3 and TiO2, and there were a large number of interface defects or oxygen defects in the samples. The BaTiO3/10 wt % TiO2 heterojunction photocatalysts have high photocatalytic activity for the degradation of tetrabromobisphenol A (TBBPA) under simulated sunlight irradiation. The interfacial defects enhance the transfer and separation efficiency of charge carriers in BaTiO3/TiO2 heterojunction photocatalysts. This technique provides a new idea for the application of BaTiO3/TiO2 heterojunction photocatalysts and other heterojunction photocatalysts in the degradation of persistent organic pollutants (POPs).

Photocatalytic performance of heterojunction S-Tyr-NDI-Tyr/TiO2 formed by self-assembled naphthalimide derivatives and titanium dioxide

In this paper, a type of heterojunction photocatalyst S-Tyr-NDI-Tyr/TiO2 was prepared by self-assembly of tyrosine-substituted naphthamide (NDA) and bonding with titanium dioxide. The self-assembly process and driving force of monomer M-Tyr-NDI-Tyr were simulated by theoretical calculation. Taking atenolol as the target pollutant, the photocatalytic performance of the heterojunction photocatalyst under visible light was studied, and the degradation products were analyzed by mass spectrometry. The environmental toxicity of photocatalytic process was evaluated by luminescent bacteria. The principle of high photocatalytic activity of S-Tyr-NDI-Tyr/TiO2 heterojunction photocatalyst was proposed by analyzing the fluorescence spectrum, photocurrent density and resistance, electron paramagnetic resonance spectrum, free radical capture experiment and energy band position of S-Tyr-NDI-Tyr/TiO2 heterojunction photocatalyst. In addition, the photocatalytic degradation of different pollutants by S-Tyr-NDI-Tyr/TiO2 heterojunction photocatalyst was also studied. This work will provide a useful example for the further development of new and efficient organic supramolecular/inorganic semiconductor composite photocatalysts.

Photocatalytic Reduction of Carbon Dioxide on TiO2 Heterojunction Photocatalysts-A Review.

The photocatalytic reduction of carbon dioxide to renewable fuel or other valuable chemicals using solar energy is attracting the interest of researchers because of its great potential to offer a clean fuel alternative and solve global warming problems. Unfortunately, the efficiency of CO2 photocatalytic reduction remains not very high due to the fast recombination of photogenerated electron–hole and small light utilization. Consequently, tremendous efforts have been made to solve these problems, and one possible solution is the use of heterojunction photocatalysts. This review begins with the fundamental aspects of CO2 photocatalytic reduction and the fundamental principles of various heterojunction photocatalysts. In the following part, we discuss using TiO2 heterojunction photocatalysts with other semiconductors, such as C3N4, CeO2, CuO, CdS, MoS2, GaP, CaTiO3 and FeTiO3. Finally, a concise summary and presentation of perspectives in the field of heterojunction photocatalysts are provided. The review covers references in the years 2011–2021.

Visible-Light-Driven g-C3N4/TiO2 Based Heterojunction Nanocomposites for Photocatalytic Degradation of Organic Dyes in Wastewater: A Review

Water pollution by organic contaminants is one of the most severe issues confronting the world today as a result of the rapid increase of industrialization, urbanization, human population growth, and advances in agricultural technologies. Several attempts have been made to address global water pollution issues by utilizing conventional wastewater treatment technologies. However, conventional wastewater treatment methods have several limitations such as low efficiency, high operation costs, generation of secondary waste, require additional chemicals as oxidants and extra energy. Therefore, Heterogeneous photocatalysis has gained a lot of attention in the degradation of persistent organic pollutants because it combines high efficiency, environmental friendliness, cheap cost, and safety. Subsequently, the designing of novel nanocomposite photocatalysts with strong visible light-harvesting ability, efficient charge separation and transportation, and superb stability is imminently desired for wastewater treatment. Recently, the notion of combining g-C3N4 with TiO2 to design high photocatalytic performance heterojunction photoactive nanocomposites for organic pollutant degradation has received a lot of attention. Meanwhile, the construction of g-C3N4/TiO2-based heterojunction nanocomposites may enhance the ability of harvesting visible light, boost charge separation and transfer efficiency, and robust photocatalytic activity. Firstly, this review concisely explained the main sources of water pollution, as well as potential treatment approaches and the fundamental mechanism of heterogeneous photocatalysis. Subsequently, the details of properties, synthesis techniques, photoactivity modification strategies, and photocatalytic applications of g-C3N4, TiO2, and g-C3N4/TiO2 heterojunction photocatalysts are presented. Following that, the recent advances aimed at improving the photocatalytic performance of various types of visible-light-driven g-C3N4/TiO2 heterojunction photocatalysts for organic pollutant degradation in wastewater are presented in detail. Finally, some concluding remarks and perspectives on the challenges and opportunities for constructing different types of g-C3N4/TiO2-based heterostructured photocatalysts are presented.

Degradation of tetracycline hydrochloride by ultrafine TiO2 nanoparticles modified g-C3N4 heterojunction photocatalyst: Influencing factors, products and mechanism insight

The unique heterojunction photocatalyst of graphite carbon nitride (g-C3N4) modified ultrafine TiO2 (g-C3N4/TiO2) was successfully fabricated by electrochemical etching and co-annealing method. However, the effects of various environmental factors on the degradation of TC by g-C3N4/TiO2 and the internal reaction mechanism are still unclear. In this study, the effects of initial pH, anions, and cations on the photocatalytic degradation of tetracycline hydrochloride (TC) by g-C3N4/TiO2 were systematically explored, and the scavenging experiment and intermediate detection were conducted to better reveal the mechanism on photocatalytic degradation of TC. The results showed that the removal efficiency of photocatalytic degradation of TC by g-C3N4/TiO2 could reach 99.04% under Xenon lamp irradiation within 120 min. The unique g-C3N4/TiO2 heterojunction photocatalyst showed excellent photocatalytic performance for the degradation of TC at pH 3∼7, and possesses outstanding anti-interference ability to NO3−, Cl−, Na+, Ca2+ and Mg2+ ions in natural waters during the photocatalytic degradation TC process. Superoxide radicals (O2•−) and hydroxyl radicals (•OH) were proved as the main reactive species for TC degradation, and the possible mechanism of the unique photocatalytic system for g-C3N4/TiO2 was also proposed. The above results can provide a reliable basis and theoretical guidance for the design and application of visible photocatalyst with high activity to degrade the actual wastewater containing TC.

In situ synthesis of an advanced Z-scheme Bi/BiOI/black TiO2 heterojunction photocatalysts for efficient visible-light-driven NO purification

Limited light absorption and severe charge recombination have been widely acknowledged as the two main obstacles restricting the application of P25 in NO photocatalytic conversion. In this work, an advanced heterojunction photocatalyst of Bi/BiOI/black TiO2 was synthesized via an in-situ solid-state chemical reduction method. The black TiO2 extended the light absorption to the full spectral region. It constructed a direct Z-scheme heterojunction with BiOI nanosheets, not only promoting the charge separation, but also preserving the strong oxidation ability of photogenerated holes in black TiO2 and strong reducing ability of photogenerated electrons in BiOI. Thus, more •O2− and •OH radical could form when Bi/BiOI/black TiO2 was subjected to visible light irradiation. Besides, the introduced Bi metal nanoparticles could also enhance the light utilization and served as a cocatalyst to accept the electrons. Therefore, enhanced NO photocatalytic oxidation activity was obtained, with the optimal sample Bi/BiOI/black TiO2 exhibiting a high NO conversion efficiency of ~70% and NOx removal of ~45%. This work may provide a refreshing perspective for the design of heterojunction photocatalysts for efficient NO photocatalytic purification and other photocatalytic applications.

Simultaneous oily wastewater adsorption and photodegradation by ZrO2–TiO2 heterojunction photocatalysts

In this work, ZrO2–TiO2 heterojunction photocatalysts were successfully synthesized using sol–gel method. The effect of ZrO2 doped into TiO2 on the retardation of the electron–hole pairs were investigated. The crystalline structure of ZrO2–TiO2 heterojunction photocatalysts was verified through x–ray diffraction (XRD) patterns and the crystallite size were found smaller compared to TiO2 and ZrO2 photocatalysts. Morphological characterization evidenced that the co–doping of ZrO2 into TiO2 has altered the particle size of TiO2 and the shape of the synthesized particle through chemical nucleation and growth process in bulk solution. The small crystallite size of the ZrO2–TiO2 heterojunction recorded the highest surface area with higher incident in the mesopores volume as confirmed by Brunauer–Emmett–Teller (BET) analysis. The adsorption–photodegradation performance of the ZrO2–TiO2 heterojunction photocatalysts on oily wastewater as model pollutant enhanced with the incorporation of small amount of ZrO2 compared to TiO2. The presence of surface adsorbed water peaks and hydroxyl groups as disclosed by Fourier transform infrared (FTIR) supported the finding of the study.

A novel microwave-assisted impregnation method with water as the dispersion medium to synthesize modified g-C3N4/TiO2 heterojunction photocatalysts

A microwave-assisted impregnation method with water as the dispersion medium was developed to prepare KCNN (K doped g-C 3 N 4 nanosheets)-TiO 2 heterojunction composite material (KCNNT). With this novel method, KCNN and TiO 2 can be evenly dispersed during synthesis to make large number of effective heterojunctions, thus offering high photocatalytic efficiency. Moreover, the use of water, instead of chemical reagents, as the dispersant makes this method both cost- and environmental-friendly. The photocatalytic degradation efficiency of RhB by KCNNT M synthesized by the microwave-assisted impregnation method was 1.23 times higher than that of KCNNT H synthesized by the thermal radiation assisted impregnation method. In addition, the photocatalytic degradation efficiency of RhB by the KCNNT 0.5M (formed with the KCNN and TiO 2 at ratio of 1:0.5) was 2.4 times higher than that of the CNT 0.5M (formed with pure g-C 3 N 4 and TiO 2 at ratio of 1:0.5), indicating the importance of modification of g-C 3 N 4 before the formation of composite materials. KCNN formed Z-type heterojunction with TiO 2 , which improved the separation efficiency of electron-hole and greatly improved the photocatalytic efficiency. The photocatalytic degradation efficiency of RhB by the KCNNT 0.5M was 4.1 times higher than that of pure g-C 3 N 4 under visible light. • The dispersant use of water, instead of chemical reagents makes this method both cost- and environmental-friendly. • The enhanced photocatalytic mechanism is a Z-scheme charge transfer pathway. • Indicating the importance of modification of g-C3N4 before the formation of composite materials. • The promising nanomaterials can be used for removal of dye pollutants.

Preparation and photocatalytic activity of g-C3N4/TiO2 heterojunctions under solar light illumination

The solar light sensitive g-C3N4/TiO2 heterojunction photocatalysts containing 20, 50, 80, and 90 wt% graphitic carbon nitride (g-C3N4) were prepared by growing Titania (TiO2) nanoparticles on the surfaces of g-C3N4 particles via one step hydrothermal process. The hydrothermal reactions were allowed to take place at 110 °C at autogenous pressure for 1 h. Raman spectroscopy analyses confirmed that an interface developed between the surfaces of TiO2 and g-C3N4 nanoparticles. The photocatalyst containing 80 wt% g-C3N4 was subsequently heat treated 1 h at temperatures between 350 and 500 °C to improve the photocatalytic efficiency. Structural and optical properties of the prepared g-C3N4/TiO2 heterojunction nanocomposites were compared with those of the pristine TiO2 and pristine g-C3N4 powders. Photocatalytic activity of all the nanocomposites and the pristine TiO2 and g-C3N4 powders were assessed by the Methylene Blue (MB) degradation test under solar light illumination. g-C3N4/TiO2 heterojunction photocatalysts exhibited better photocatalytic activity for the degradation of MB than both pristine TiO2 and g-C3N4. The photocatalytic efficiency of the g-C3N4/TiO2 heterojunction photocatalyst heat treated at 400 °C for 1 h is 1.45 times better than that of the pristine TiO2 powder, 2.20 times better than that of the pristine g-C3N4 powder, and 1.24 times better than that of the commercially available TiO2 powder (Degussa P25). The improvement in photocatalytic efficiency was related to i) the generation of reactive oxidation species induced by photogenerated electrons, ii) the reduced recombination rate for electron-hole pairs, and iii) large specific surface area.

In situ synthesis of ultrafine TiO2 nanoparticles modified g-C3N4 heterojunction photocatalyst with enhanced photocatalytic activity

To improve the redox performance and light absorption property, the 2D/0D g-C3N4/TiO2 heterojunction photocatalyst were successfully fabricated by co-annealing process based on melamine powder and ultrafine TiO2 nanoparticles (about 9.87 nm) obtained from electrochemical etching technology. The surface micromorphology, crystal structure, basic element composition, chemical structure, specific surface and optical performance were analyzed by SEM-EDS, TEM, HR-TEM, XRD, XPS, FTIR and Ultraviolet–visible diffuse reflection spectra (UV–vis DRS). The photocatalytic performance of g-C3N4/TiO2 photocatalyst was assessed by the degradation of tetracycline hydrochloride (TC) under simulated sunlight irradiation. The results showed that the obtained TiO2 powder had extremely smaller particle size and higher photocatalytic activity than commercial P25. The coupling of 0D TiO2 nanoparticles and 2D g-C3N4 nanosheet further promoted the visible light absorption performance of TiO2. The unique g-C3N4/TiO2 heterojunction photocatalyst exhibited remarkable photocatalytic performance for the degradation of TC, whose degradation rate could reach to 99.40% under 120 min irradiation. The kinetic constant of the g-C3N4/TiO2 photocatalyst was 1.48 times of that of TiO2. The ESR results confirmed ·OH and ·O2– radicals produced in the photocatalytic process. This work could provide an effective reference for the fabrication of ultrafine TiO2 powder and binary heterojunction photocatalyst with excellent photocatalytic activity for organic pollutants degradation in water purification.

MOF-derived the direct Z-scheme g-C3N4/TiO2 with enhanced visible photocatalytic activity

In order to produce a photocatalyst with increased visible photocatalytic ability, MIL-125 and melamine were selected as raw materials to prepare Z-scheme g-C3N4/TiO2 heterojunction photocatalyst using a simple calcination method. TEM, HRTEM, XRD, FTIR, EDS, and UV–vis absorption spectra were employed to investigate the prepared specimens. The visible-light catalytic property was examined via the degradation of methylene blue (MB). The recombination and separation activity of electrons and holes (h+/e−) were explored by the transient photocurrent response (TPR) and PL spectra. In contrast with plain TiO2 and g-C3N4, the g-C3N4/TiO2 photocatalyst exhibited increased photocatalytic activities when exposed to visible-light irradiation. With the addition of g-C3N4 at 8 wt%, the Z-scheme g-C3N4/TiO2 heterojunction performed best in the photocatalytic test toward MB dye at a degradation rate of 97.7%. Under visible-light irradiation, the Z-scheme heterojunction between g-C3N4 and TiO2 enables the high-efficient segregation of photogenic electrons and holes (h+/e−), leading to the increased photocatalytic ability. Meanwhile, the large specific surface area of the composite photocatalyst is conducive to the adsorption of the contaminant on the catalyst surface, which has an important effect on the catalytic reaction.

Enhanced organic pollutant photodegradation via adsorption/photocatalysis synergy using a 3D g-C3N4/TiO2 free-separation photocatalyst

The three dimensions (3D) g-C3N4/TiO2 heterojunction photocatalyst has been synthesized and exhibits efficient pollutant degradation performances. The degradation efficiency of methylene blue (MB) and phenol is 4.0 and 4.5 times as high as bulk g-C3N4 in static system. In dynamic system, the pollutant can be continuously degraded without separation, and it is very stable for 90 h with a removal rate of 16.0%. The enhanced activity is mainly attributed to the 3D structure and heterojunction of g-C3N4/TiO2. The 3D structure can not only effectively improve the adsorption-enrichment capability, but also supply multidimensional mass and electron transfer channels. Meanwhile, the heterojunction can promote the separation and migration of the photo-generated carriers. Therefore, the 3D g-C3N4/TiO2 heterojunction photocatalyst with separation free can facilitate the potential application in the treatment of water pollution.

Multiphase TiO2 surface coating g-C3N4 formed a sea urchin like structure with interface effects and improved visible-light photocatalytic performance for the degradation of ibuprofen

In this research, we did not use any template, but a prickly structure urchin like morphology made of composite TiO2/g-C3N4 was synthesized by a one-step solvothermal method. It is generally reported that TiO2 is a pure phase, besides, the photocatalytic effect of multiphase TiO2 will be better. After the g-C3N4 was successfully loaded on the TiO2 surface, the morphology did not change. The special sea urchin morphology provides more active sites for catalysis. The band gap becomes smaller, because two materials were combined to form an interface effect. Meanwhile, it could effectively separate electron hole pairs, and promote charge transfer efficiency. More active substances were produced under visible light, such as superoxide radicals and holes. The scavenging experiment further confirms that superoxide radicals and holes play an important role in the catalytic process. The photocatalytic degradation of ibuprofen under visible light was improved. A possible enhanced photocatalytic mechanism of g-C3N4/TiO2 heterojunction photocatalysts was proposed.

In situ hydrothermal synthesis of g-C3N4/TiO2 heterojunction photocatalysts with high specific surface area for Rhodamine B degradation

Semiconductor-based photocatalysis is a promising method for degradation of environmental pollutants, but the activity of most widely used photocatalysts such as titania (TiO2) is still unsatisfactory under visible light. Herein, we synthesized a highly efficient visible-light-responsive heterojunction catalysts based on graphitic carbon nitride (g-C3N4) and TiO2. The g-C3N4/TiO2 heterojunction composites with high specific surface area were prepared via in situ hydrothermal synthesis followed by calcination, using titanium tetrachloride (TiCl4) and melamine as precursors. Interesting, HCl from the hydrolysis of TiCl4 served as the proton source to acidify the melamine. The g-C3N4/TiO2 heterojunction composites exhibited higher photocatalytic performance for decomposition of Rhodamine B (RhB) than pure g-C3N4 or TiO2 under visible light irradiation. The high activity can be ascribed to the high specific surface area (up to 115.6m2g−1) of the g-C3N4/TiO2 composites and a synergistic heterojunction structure between TiO2 and g-C3N4. Moreover, the photocatalytic performances of the g-C3N4/TiO2 composites rely on the content of melamine in the synthesis precursors: with an optimum melamine content (3g for 0.5mL of TiCl4), the sample showed the highest photocatalytic performance, which is superior to pure TiO2 and g-C3N4 by a factor of 18.7 and 3.5, respectively. Active species trapping experiments revealed that superoxide radicals and photogenerated holes played crucial roles in the photocatalytic reactions. The results will provide new ideas for the smart design and development of g-C3N4-based highly active photocatalysts with ultrahigh specific surface area for environmental and energy applications.

Template-free preparation of macro/mesoporous g-C3N4/TiO2 heterojunction photocatalysts with enhanced visible light photocatalytic activity

Mesoporous photocatalytic materials with macroporous structures have attracted more and more attention because of their textural mesopores and intrinsic interconnected pore networks, which are able to efficiently transport guest species to framework binding sites. In this work, macro/mesoporous g-C3N4/TiO2 heterojunction photocatalysts were fabricated without templates or additives by a facile calcination method using tetrabutyl titanate and melamine as the feedstocks. Photocatalytic experiments of the as-prepared samples were measured by the photocatalytic oxidation degradation of RhB solution at room temperature under visible light irradiation. The results indicated that the melamine content in the precursors had an important influence on photocatalytic activity of the as-prepared samples. At the optimal loading content, the apparent reaction rate constant (k) was 47.8×10−3min−1 for RhB degradation, exceeding that of pure TiO2 (6.6×10−3min−1) and g-C3N4 (15.2×10−3min−1) by factor of 7.2 and 3.1 respectively. The improved photocatalytic activity was attributed to high surface area and heterostructure formation of g-C3N4/TiO2 composites. The trapping experiment results showed that O2− and h+ were main active species in the decomposition of RhB. A possible enhanced photocatalytic mechanism of g-C3N4/TiO2 heterojunction photocatalysts was proposed.