Low Temperature Carbonization Process Research Articles

Efficient removal and reusage of acid soluble oil in waste H2SO4 of isobutane alkylation by low-temperature carbonization process

Waste H2SO4 from industrial isobutane alkylation, a hazardous thick liquid with a high concentration of acid soluble oil (ASO) impurities, poses challenges in the regeneration process. Herein, an innovative low-temperature carbonization process was proposed to convert waste H2SO4 into the regenerated concentrated H2SO4 and sulfonated activated carbon materials (SACMs) under mild reaction conditions. The optimal reaction temperature is identified at 423.15 K with the highest TOC removal of 90.57%. The high-purity regenerated H2SO4 with a concentration of 95% as a catalyst for isobutane alkylation exhibits excellent catalytic performance with 94.54 research octane number (RON) of the alkylate. SACMs, characterized as a novel porous carbon material with plentiful hydroxyl, carboxylic acid, and sulfonic acid functional groups, demonstrate an efficient catalytic activity in the dimerization of lactic acid to produce lactide with a yield of 46.95%. Hopefully, the novel recovery process provides a promising application to optimize the regeneration process of waste H2SO4 from industrial isobutane alkylation.

Low temperature carbonization, smoke suppression and durable flame retardancy of cotton fabric spray-assisted coated by phosphorus nitrogen silicon composite system

To solve the problems of flammability, smoldering, smoking and flame retardant durability of cotton fabric, flame retardant fininshing was executed using spray assisted self-assembly method, and P/N/Si synergistic flame retardant system was constructed by polyethylene imine (PEI), phytic acid (PA) and 3-aminopropyltriethoxysilane (APTES). Cotton cellulose carbonized at low temperature prompting by PA catalytic effect, and this cooperated with PEI thermal decomposition to endow cotton fabric with flame retardancy and smoking suppression by reducing its pyrolysis rate at high temperature and lessening combustible products. Meanwhile APTES as silane coupling agent further improved its flame retardant durability and smoke suppression effect. The synchronous thermal analysis results indicate that cotton fabrics treated by PA/PEI/APTES composite system present significant low-temperature carbonization trend, and their initial decomposition temperatures advance by 46.5℃-75.9℃. Moreover, they form 4.6 %-44.9 % aromatic structure char through dehydration and carbonization reactions during the low-temperature carbonization process, improving their thermal stability at high temperature, and their after-flame and smoldering phenomena disappear. The damaged length of treated fabric with five layers reduces to 5.0 cm, its limiting oxygen index reaches 33.7 %, and it presents excellent flame retardant durability and smoke suppression effect. This low-temperature carbonization mechanism possesses importantly innovative significance for the flame retardant finishing of cotton fabric, and it not only more actively guides the selection of flame retardants to make them match with the material required, but provides a new thinking method for flame retardant material research in the future.

Manipulating singlet oxygen generation on Co nanoclusters-confined g-C3N4 macroscopic beads for boosted water decontamination

Reducing the migration distance of reactive oxygen species (ROS) and enhancing interfacial electron transfer represent effective approaches for enhancing the reactivity of heterogeneous catalysts, albeit still posing significant challenges. Herein, we successfully synthesized ultrasmall cobalt nanoclusters-confined g-C3N4 macroscopic beads with N-doped carbon dots (Co/NC@CN beads). Compared to unconfined Co/C and Co/C@CN beads, Co/NC@CN beads demonstrated remarkable utilization efficiency of PMS (84.3%), achieving complete degradation of TC within 20 min at a rate of 162.1 min-1·M-1, surpassing most reported catalysts. Besides, Co/NC@CN beads predominantly generated singlet oxygen (1O2), ensuring efficient removal of micropollutants with resistance to pH and complex water bodies. Experiments have proven that the strong interaction between Co clusters and g-C3N4 beads containing NC dots facilitated the generation of interfacial electron transfer by optimizing the electronic structure of Co nanoclusters, thereby Co/NC@CN beads could capture electrons from tetracycline (TC) and PMS molecules towards dissolved oxygen (DO) to form O2·-, which subsequently converted into 1O2. More importantly, the efficiency of the flow-through unit in the continuous degradation of TC with zero discharge was substantiated by long-term experiments, and its performance could be restored through a straightforward low-temperature carbonization process. This study offers a universal design framework for the creation of various confined macroscopic beads, enabling the achievement of highly effective wastewater treatment.

Development of Modified Mesoporous Carbon from Palm oil Biomass for Energy Storage Supercapacitor Application

Energy storage system research including battery and supercapacitor devices has been studied to increase efficiency, lower their cost and improve environmental friendliness. Supercapacitor (SC) device offers high transient response and power density which suitable for many applications. The electrodes in supercapacitor device usually produced from highly porous carbon materials. In this study, the modified mesoporous carbon was produced from Palm empty fruit bunch (EFB) biomass. The production of mesoporous carbon was done using a low-temperature hydrothermal carbonization process. The mesoporous carbon from EFB biomass has shown good properties in terms of high surface area and porosity. To improve the electrical conductivity of the carbon the modification by nitrogen doping with ammonium chloride and urea was studied. The effect of different nitrogen sources on surface area and pore properties were reported. The modified mesopore carbon was tested in a symmetrical swagelok supercapacitor cell to evaluate the specific capacitance and efficiency using galvanostatic charge-discharge method. The modified mesoporous carbon with urea doped exhibits the highest specific capacitance of 121 F g-1 at current loading of 0.1 A g-1 in an aqueous 1M H2SO4 electrolyte. The modified mesoporous carbon with urea doped has lower internal resistance due to nitrogen from urea enhance the electronic conductivity of the electrodes and thus increase the supercapacitor performance.

Novel 3D carbon fibers derived from Luffa wastes for oil/water separation

In this study, the 3D structure of carbon fibers (CFs) was prepared from Luffa sponge wastes by H3PO4 impregnation with various ratios and a low-temperature carbonization process at 500 °C in a nitrogen atmosphere. The H3PO4-treated Luffa sponge had higher thermal stability and carbonic yield (∼60–70%) than neat-Luffa (∼21%). Characterization analyses exposed that the synthesized CFs derived from H3PO4-treated Luffa exhibited oleophilic and hydrophobic carbonic nature with 3D sponge skeletal, reflecting an ideal structure for oil sorption. The engine oil sorption properties on the CFs were studied by varying the contact time. The engine oil sorption equilibrium data for 3D CFs samples was explained by the pseudo-second-order and intraparticle diffusion models. The equilibrium oil sorption capacities of 3D CFs were as large as 23.1 ± 0.4 g/g for engine oil, 23.7 ± 1.0 g/g for gasoline, 28.1 ± 1.0 g/g for almond oil, and 29.2 ± 0.8 g/g for pomegranate seed oil in 20 min. Moreover, the optimized 3D CFs can be selectively for oil/water separation applications, such as high capacities for various oils, fast kinetic sorption, and reusability (>6 cycles). This research presented a facile and cost-effective process for the 3D CFs through recycling Luffa sponge wastes for rapid oil sorption.

Single-Step Hydrothermal Synthesis of Biochar from H3PO4-Activated Lettuce Waste for Efficient Adsorption of Cd(II) in Aqueous Solution.

Developing an ideal and cheap adsorbent for adsorbing heavy metals from aqueous solution has been urgently need. In this study, a novel, effective and low-cost method was developed to prepare the biochar from lettuce waste with H3PO4 as an acidic activation agent at a low-temperature (circa 200 °C) hydrothermal carbonization process. A batch adsorption experiment demonstrated that the biochar reaches the adsorption equilibrium within 30 min, and the optimal adsorption capacity of Cd(II) is 195.8 mg∙g−1 at solution pH 6.0, which is significantly improved from circa 20.5 mg∙g−1 of the original biochar without activator. The fitting results of the prepared biochar adsorption data conform to the pseudo-second-order kinetic model (PSO) and the Sips isotherm model, and the Cd(II) adsorption is a spontaneous and exothermic process. The hypothetical adsorption mechanism is mainly composed of ion exchange, electrostatic attraction, and surface complexation. This work offers a novel and low-temperature strategy to produce cheap and promising carbon-based adsorbents from organic vegetation wastes for removing heavy metals in aquatic environment efficiently.

Evolution mechanism of cyclized structure of PAN-based pre-oxidized fiber during low temperature carbonization process

The low temperature carbonization process is an important stage to realize the structural transition from the organic cyclized structure of PAN based pre-oxidized fiber to the inorganic pseudo-graphite structure of the ultimate carbon fiber. In the present paper, the evolution mechanism of cyclized structure and aggregation structure of PAN stabilized fiber during low temperature carbonization was studied by means of TGA, 13C-NMR, XRD, XPS and Raman. The results indicated that when the heat-treated temperature was lower than 450 °C, the mainly chemical reactions were the dehydrogenation and pyrolysis reactions in acyclic linear molecular chain or partial cyclized structure. At this stage, the growth of cyclized structure was not obvious. While the original ordered structure was destroyed gradually and the internal stress increased significantly. It induced the cyclized structure to be further oriented. When the temperature was higher than 450 °C, the polycondensation and reconstruction in aromatic heterocyclic structure was more important. The early aromatic heterocycles had many different structural scales, poor homogeneity and many defects in the heterocycles. At this stage, a new pseudo-graphite crystalline structure gradually formed and the d-spacing of graphite layer decreased slightly and crystallites size increased slowly with the increase of heat-treated temperature. When the temperature was higher than 550 °C, the pseudo-graphite base structure gradually formed. The d-spacing were further reduced slightly, and the crystallites size increased slowly. A new ordered basis structure was gradually developed into carbon fiber.

Effect of Electrolyte Composition on the Performance of Coal Char-Derived Carbon Supercapacitors

Research regarding supercapacitors has vastly grown over the past decade. The advantages of supercapacitors include high power density, rapid charge/discharge capability, and a long cycle life. Current applications of supercapacitors are limited by the need to develop new, low-cost electrode materials for electric double layer capacitors and pseudocapacitors [1]. Coal char is the solid product of a low-temperature coal carbonization process, and is currently used primarily as an ultra-low-cost fuel for electric power generation. As such, coal char consists mainly of hard carbons and ash [2]. Upon ash removal, the hard carbons in coal char may serve as a promising, low-cost, supercapacitor electrode material. This research will present the use of inexpensive coal char as an electrode material for supercapacitors, with particular focus on the effects of various electrolyte compositions on the performance of coal-derived carbon supercapacitors.Electrolyte composition plays a large role in the electrochemical properties of a supercapacitor, affecting: ion interactions with electrode surface functional groups; electric double layer capacitance; thermal stability; and allowable voltage range. In this work, bituminous grade coal char from a Utah mine is pulverized, pyrolyzed, and washed in a base solution followed by an acid solution to remove residual ash. SEM imaging and BET surface area measurements are used to characterize the coal. The purified coal char is mixed into a slurry of coal char, Super P binder, and dimethylformamide, then applied on a stainless-steel plate to create supercapacitor electrodes. Three-electrode open-cell electrochemical measurements are used to characterize the supercapacitor performance of the coal char in varying electrolyte solutions using a Gamry Interface 1000E potentiostat. The different electrolytes explored include: aqueous acid 0.5 M H2SO4, aqueous base 6 M KOH, and aqueous neutral solutions 0.5 M Na2SO4, 4 M LiNO3, water-in-salt electrolyte using 12.5 M NaClO4, . Voltage range, specific capacitance, electrochemical impedance, and charge-discharge characteristics of the coal char in the different electrolytes are characterized by cyclic voltammetry, chronopotentiometry, and electrochemical impedance spectroscopy measurements. The results provide important insight into the optimal electrolyte composition for use with coal char supercapacitor electrodes, and contribute to current understanding of electrode-electrolyte interactions in carbon supercapacitors.This work is supported in-part by NSF Award #1742696.Reference1.Rakesh Kumar Gupta, Mukul Dubey, Parashu Kharel, Zhengrong Gu, Qi Hua Fan, Biochar activated by oxygen plasma for supercapacitors, Journal of Power Sources, Volume 274, 2015, Pages 1300-1305.2. H. H. Schobert, Coal; The Energy Source of the Past and Future, pg. 9, American Chemical Society, Washington (1987). Figure 1

Tailoring graphitic nanostructures in hard carbons as anode materials achieving efficient and ultrafast sodium storage

Hard carbons appear to be promising anode candidates in high-performance sodium-ion batteries (SIBs) for large-scale stationary energy storage due to their large interlayer distance and amorphous structure, which facilitate sodium ions insertion/desertion. However, several major hurdles to address are poor rate performances and the low initial coulombic efficiency (ICE). Herein, a facile strategy to tailor hard carbons with graphitic nanostructures and rational specific surface area is proposed to improve sodium storage. Resin-derived carbon nanobroccolis (CNB) with in situ decorated graphitic nanostructures have been successfully synthesized by self-assembly and low-temperature catalytic carbonization process. As a result, attribute to in situ tailored graphitic nanostructures in hard carbons and rational specific surface area, CNB electrodes possess less charge transfer resistance and excellent sodium ions diffusion kinetics and successfully achieve fast and efficient sodium storage. When used as anode for sodium-ion batteries, CNB electrodes exhibit excellent high-rate capability of 137 mAh g−1 at 1000 mA g−1 and enhanced ICE of 52.6%. Our strategy reported here opens a door to design high-performance carbon anode materials for SIBs particularly focusing on efficient sodium ions storage and fast sodium ions diffusion.

The Role of Tension and Temperature for Efficient Carbonization of Polyacrylonitrile Fibers: Toward Low Cost Carbon Fibers

We report the production of automotive grade carbon fibers in a low temperature carbonization furnace by making use of the influence of various levels of tensions and temperatures on polyacrylonitrile (PAN) precursor fibers. The experiments were performed at two different temperatures during a low temperature carbonization process to understand the effect of differences in temperature as well as tension. The effect of oxidative stabilization and carbonization processes on the structure, mass retention, and mechanical properties of precursor fibers was analyzed. Fibers were collected from each zone of the low and high temperature furnaces, and physical properties were measured for carbon fibers along with precursor and oxidized fibers. The infrared studies revealed the variation in the chemical structure of the fibers during the stabilization, and the aromatization index of 65.5% was calculated from thermal studies of the stabilized fibers. It was found that an increase in tension during low temperature (L...

Biochar Preparation from Simulated Municipal Solid Waste Employing Low Temperature Carbonization Process

This paper presents an investigation on carbonization process of simulated municipal solid waste (MSW). Simulated MSW consists of a representative of food residue (68%), plastic waste (20%), paper (8%), and textile (4%). Laboratory-scale carbonization was performed in this study using a vertical-type pyrolyzer varying carbonization temperature (300, 350, 400, and 450 °C) and heating rate (5, 10, 15, and 20 °C/min). Appearance of the biochar product was in black and the volume was significantly reduced. Low carbonization temperature (300 °C) might not completely decompose plastic materials in MSW. Results showed that the carbonization at the temperature of 400 °C with the heating rate of 5 °C/min was the optimal condition. The yield of biochar from the optimal process was 50.6% with the heating value of 26.85 MJ/kg. Energy input of the process was attributed to water evaporation and the decomposition of plastics and paper. Energy output of the process was highest at the optimal condition. Energy output and input ratio was around 1.3-1.7 showing the feasibility of the carbonization process in all heating rate condition.

TiO2/EDTA-rich carbon composites: Synthesis, characterization and visible-light-driven photocatalytic reduction of Cr(VI)

TiO2/EDTA-rich carbon composites (TiO2/EDTA-RC) have been successfully synthesized via a low temperature carbonization process. TiO2/EDTA-RC exhibits marked absorption of visible light and excellent photoreduction of Cr(VI) activity under visible light irradiation (λ>420nm). Due to the high carboxyl group content and strong coordination ability of EDTA, TiO2-EDTA complex can be easily fabricated between EDTA incorporated in carbon sheet and titanol group on the surface of TiO2. TiO2-EDTA complexes on the surface of TiO2/EDTA-RC, the LMCT complex, are responsible for the prominent photoreduction of Cr(VI) properties of TiO2/EDTA-RC under visible light irradiation. In addition, the unique structure of TiO2/EDTA-RC is also propitious to the visible-light photocatalytic reduction of Cr(VI). Carbon sheet of TiO2/EDTA-RC acts as a supporter. TiO2 nanoparticles and EDTA homogeneously disperse into the carbon sheet supporter and form the TiO2-EDTA complexes, which can avoid the aggregation of TiO2 nanoparticles in the aqueous solution and provide more photocatalytic reaction points for the reduction of Cr(VI).

Consecutive preparation of hydrochar catalyst functionalized in situ with sulfonic groups for efficient cellulose hydrolysis

Hydrochars in situ functionalized with –SO3H groups were generated from kenaf core via a low-temperature hydrothermal carbonization process of 105 °C with a consecutive catalysis of H2SO4. The micro-morphology of the hydrochars was strongly affected by the sulfuric acid concentration. Sphere-like particles with size varying between 200 nm and 1 μm were obtained when the acid concentration was 52 wt%. Acid density of the hydrochar increased with the H2SO4 concentration increasing. The presence of considerable acidic groups of –SO3H, –COOH, and –OH on the surface of hydrochars was evidenced by Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy. The hydrochar obtained can be used directly for effective catalytic hydrolysis of cellulose without any post-modification. This study proposed a promising sustainable and cost-effective route for facile production of acidic hydrochar from crude plant with tunable properties.

Modeling of Low-Temperature Carbonization of Sulfur-Bearing Oil Shales in a Fluidized-Bed Retort

A mathematical model of the process of low-temperature carbonization of sulfur-bearing oil shales in a fluidized-bed retort, which takes account of the characteristics of hydrodynamics and heat exchange in the thermal shale decomposition process as well as the kinetics of thermal degradation of the organic matter, is developed. A block diagram of the calculation algorithm and the results of numerical experiment based on the developed mathematical model are presented. It is shown that the properties of the sulfur-bearing shale and the conditions of the low-temperature carbonization process affect the parameters of the fluidized-bed retort.

미분쇄 탄소섬유가 첨가된 피치계 탄소섬유기반 기체확산층용 탄소종이 특성

본 연구에서는 피치계 탄소섬유기반 탄소종이에 바인더 피치와 PAN계 미분쇄 탄소섬유를 첨가하여 저온탄화를 통해 재함침된 탄소종이를 제작하였으며, 미분쇄 탄소섬유의 첨가가 탄소종이의 기계적 및 전기적 특성과 열전도도에 미치는 영향을 알아보았다. 실험 결과, 인장강도는 미분쇄 탄소섬유 함량 10 wt.%부터 20 wt.%까지 첨가하였을 때 크게 증가하였다. 또한, 미분쇄 탄소섬유 함량이 증가함에 따라 계면접촉저항은 감소하였으며, 전기전도도 및 열전도도는 증가하였다. 이러한 결과는 미분쇄된 탄소섬유의 첨가가 탄소종이의 밀도를 증가시킴에 따라 전기적 및 열적 전달 경로가 형성되었기 때문이라고 판단된다. In this work, the pitch-based carbon paper (P-CP) was prepared by re-impregnating of binder pitches and PAN-based milled carbon fibers (MCF) at low temperature carbonization process. The influence of MCF content on physicochemical properties of MCF/P-CP was investigated. As a result, the tensile strength of MCF/P-CP was increased sharply from 10 wt.% to 20 wt.% of MCF. Also, the increase of MCF content led to the decrease of interfacial contact resistivity and the improvement of electrical and thermal conductivity of MCF/P-CP. These results were probably due to the increase of density of MCF/P-CP, resulting in the formation of electrically and thermally conductive paths of the carbon paper.

Enhanced visible-light photocatalytic activity of carbonate-doped anatase TiO2 based on the electron-withdrawing bidentate carboxylate linkage

Carbonate-doped anatase TiO2 photocatalysts were prepared by a conventional sol-gel method and subsequent xerogel carbonization process in hypoxic atmosphere. Acetic acid was used as the hydrolysis inhibitors of titanium butoxide (TBOT) and the carbon source was the organic species produced during the synthesis of TiO2 particles. Via a low-temperature (≤300°C) carbonization process, the carboxylate ligands from the chelated acetic acid molecules can be retained and transformed into the bidentate carboxylate linkage between the amorphous carbonate dopants and TiO2 lattice. The strong electron-withdrawing bidentate carboxylate ligands can induce valence band (VB) tail states to narrow the bandgap of TiO2, as confirmed by attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) analyses. Moreover, the carbonate dopants can serve as photosensitizer to absorb visible-light and help to promote the charge carriers’ separation through cooperation with bulk/surface defects of TiO2. The synergistic effects can significantly enhance the visible-light photocatalytic activities of TiO2 for phenol degradation (λ≥420nm). The band structure and possible photocatalytic mechanism of the carbonate-doped TiO2 were thus elucidated.

Lignin-Based Fabrication of Co@C Core–Shell Nanoparticles as Efficient Catalyst for Selective Fischer–Tropsch Synthesis of C5+ Compounds

Novel Co@C core–shell nanoparticles were prepared by a straightforward low-temperature carbonization process. The industrially available lignin was used as a low-cost biorenewable carbon source for the first time. The products were characterized by X-ray diffraction, energy-dispersive X-ray spectrometry, transmission electron microscopy, nitrogen adsorption–desorption, and Raman spectrum. The results showed that the synthesized Co@C catalysts had a well-defined core–shell structure with a moderate degree of graphitization, and the metal Co nanoparticles with the sizes of 20–150 nm were wrapped by several layers of graphitic carbon. This unique core–shell structure is useful in a Fischer–Tropsch reaction since it can provide high adsorption space and the graphite carbon layer defects are beneficial for H2 dissociative adsorption. Furthermore, the shell of graphitic carbon layers could restrict the aggregation of the cobalt nanoparticles during the activation and reaction processes. Fischer–Tropsch synthesis results showed that the Co@C core–shell catalysts had a high catalytic performance with the highest C5+ selectivity up to 56.8%, which is much higher compared with the traditional Co/AC catalyst (46.2%).

One-step synthesis of Fe3O4/carboxylate-rich carbon composite and its application for Cu(ii) removal

A magnetically separable adsorbent, Fe3O4/carboxylate-rich carbon composite was synthesized via a facile one-step low temperature carbonization process.

Lignite temperature distribution during low temperature carbonization process in an industrial width carbonization furnace

Highly efficient industrial carbonization furnace with a width of 500mm was established in this study. The characteristics involving temperature increase, variation rules for the thermal conductivity of coal, and the temperature distribution model of the coking chamber in a low temperature carbonization process of lignite performed in the furnace were studied. The results showed that the temperature profile of coking chamber could be divided into three zones: the near, middle, and remote zones. The distinguishing index between near and middle zones was a low-temperature-constant (80–100°C) stage. ∂2T∂t2=0,∂T∂t=n were the distinguishing indices between the middle and remote zones. When the lignite was carbonized in a single heat source furnace wall coking chamber, the temperature distribution followed the Chen–Clayton equation. Moreover, the effective thermal conductivity coefficient of coal was affected by the carbonization time and heat transfer distance, which exhibited a unimodal distribution during the carbonization process. Furthermore, the classic one-dimensional unsteady temperature distribution model with heat resource factor and the correction equation of heat temperature thermal conductivity were established. After being corrected, the calculated temperature curve was consistent with the measured temperature curve. The model was confirmed by the residual analysis and the error points were in well agreement with the normal distribution.

TiO2/carboxylate-rich porous carbon: A highly efficient visible-light-driven photocatalyst based on the ligand-to-metal charge transfer (LMCT) process

A novel visible-light-driven photocatalyst based on TiO2/carboxylate-rich porous carbon composite (TiO2/CRPC) was successfully synthesized by low temperature carbonization process in air. Sodium gluconate plays a crucial role in the formation of TiO2/CRPC. Different functional groups of sodium gluconate play synergetic roles in the formation of TiO2/CRPC. XRD and Raman spectra studies indicated that there are two different TiO2 crystalline phases existing in TiO2/CRPC, which are anatase and brookite, and the CRPC is amorphous. Via FT-IR and XPS spectra investigations, it was demonstrated that carboxylate group, the ligand-to-metal charge transfer (LMCT) forming functional group, was solidified into the CRPC and form the LMCT complex on TiO2 surface through the fabrication of TiO2/CRPC. Compared with the pure TiO2, TiO2/CRPC exhibit enhanced absorption in the UV and visible light region around 260–600nm. The strong absorption in the visible light region gives TiO2/CRPC advantages over pure TiO2 for the degradation of organic pollutants. TiO2/CRPC can activate O2 in air under mild conditions and exhibit excellent visible-light-driven photocatalytic activities. However, TiO2/C composite obtained by using glucose instead of sodium gluconate exhibits poor photocatalytic activity, which demonstrated that carboxylate–TiO2 complexes are responsible for the prominent photocatalytic properties of TiO2/CRPC under visible light irradiation.