Collection of Removal of Pollution in Water(202312)
Preparation of highly efficient and stable photocatalysts is crucial for the development of photocatalysis technology. In this study, the method of ultrasonic-assisted deposition and low-temperature calcination was used to prepare MoS2/g-C3N4 S-type heterojunction photocatalyst (MGCD). Effects of the phase structure, micro-morphology, optical absorption performance, X-ray photoelectron spectroscopy, electrochemical AC impedance, and photocurrent of the materials on the photocatalytic activity were comprehensively investigated. The results show that, after ultrasonic-assisted deposition-calcination treatment, MoS2 microspheres were broken, dispersed and combined on the surface of g-C3N4 nanosheets, and formed a kind of heterojunction. Under visible light, the degradation rate of 5%MGCD (with 5% MoS2 addition) for Rhodamine B (RhB) reached 99% in 20 min, and still reach 95.2% when the sample was reused for 5 times, showing good photocatalytic performance and stability. Further analysis from the point of view of the formation of built-in electric field shows that the band bending caused by built-in electric field, coupled with MoS2 and g-C3N4 in heterojunction, can effectively guide the directional migration of carriers, which can efficiently promote the separation of photogenerated carriers, thus improving the efficiency of photocatalytic reaction. Free radical capture experiment of heterojunction photocatalyst reveals that O2- and ·OH are the main active species in the catalytic degradation of RhB, followed by H+.
Methane is the second greenhouse gas contributing greatly to global warming, about 80 times of CO2. Considering background of global warming and atmospheric methane growth, to catalyze total oxidation of atmospheric methane is of great importance to mitigate greenhouse effects and slow this global warming. However, catalytic oxidation of methane has always been a big challenge due to its high structural stability. In this article, research progress in total oxidation of methane under thermal-, photo- and photothermal-catalysis was reviewed. High temperature in thermal catalysis increases the energy loss and accelerates the deactivation of catalysts speedingly. Therefore, development of catalysts that oxidize methane under moderate temperatures is the main research interests. Photocatalysis provides a way to eliminate methane at ambient conditions with the assistance of solar energy, but the reaction rates are lower than that in thermal catalysis. It is worth mentioning that photothermal catalysis, developed in recent years, can achieve efficiently catalytic total oxidation of methane under mild conditions, showing a high potential application prospect. This article reviews development of three modes of catalysis, analyzes their different reaction mechanisms, advantages and disadvantages under different reaction conditions. Finally, prospects and challenges of this catalytic total oxidation are pointed out, which is expected to provide references for future research on this field.
Indoor formaldehyde (HCHO) pollution has become one of the major issues affecting human health. Catalytic formaldehyde oxidation technology employing oxygen as oxidant has received extensive attention owing to its mild conditions and nontoxic byproducts, but developing affordable and effective catalysts remains a significant hurdle. In this work, α-Ni(OH)2 was prepared through one-step hydrothermal method and its catalytic formaldehyde oxidation mechanism was investigated. The greatest catalytic formaldehyde elimination rate of 71.2% was demonstrated by α-Ni(OH)2 at room temperature, which was made with water as the solvent and nickel nitrate as the nickel source. In situ DRIFTS and theoretical calculations revealed that, due to abundant hydroxyl functional groups on the surface of α-Ni(OH)2, there was strong interaction between adsorbed formaldehyde and hydroxyl group on the surface of α-Ni(OH)2, which promoted formaldehyde activation and achieved oxidation of formaldehyde without oxygen. On the other hand, the XPS spectra of α-Ni(OH)2 treated under different conditions confirmed that the active sites of catalytic formaldehyde oxidation were Ni3+, and oxygen accelerated the recovery of Ni3+ active sites. The surface hydroxyl group of α-Ni(OH)2 cooperated with the Ni3+ active sites achieved excellent catalytic efficiency of formaldehyde oxidation, which was obviously different from the traditional formaldehyde oxidation path with oxygen dissociation as the speed control step. Our work presents a new formaldehyde oxidation pathway controlled by synergy of surface hydroxyl and active sites, and offers a theoretical foundation for the actual use of catalytic formaldehyde oxidation.
In a high vacuum environment, some organic molecular pollutants such as hydrocarbon and siloxane are released by spacecraft materials and deposited on the surface of the sensitive parts of spacecraft devices, which has become an important adverse factor restricting the development of long-life and high-performance spacecraft. Zeolite molecular adsorber coating can effectively collect spatial contaminations in real time, but the adsorption mechanism is not clear. To deeply analyze the adsorption mechanism of zeolite on the spatial contaminations, the adsorption behaviors of NaY zeolite including adsorption isotherms, adsorption heat curves and density distributions on three typical contaminations, toluene(C7H8), dimethyl phthalate (C10H10O4), octamethyl cyclotetrasiloxane (C8H24O4Si4), were calculated by the Grand Canonical Monte Carlo method in this work. The NaY zeolites and pollutant models were successfully constructed, and the rationality of the models was verified by comparing simulated data with experimental ones. These results indicated that all three classic molecules can be adsorbed by NaY zeolite in the ultra-high vacuum condition. The saturated adsorption capacity decreases in the order of C7H8>C10H10O4>C8H24O4Si4, which is significantly related to the molecule sizes and structures of contaminations. The saturated adsorption amount of C8H24O4Si4 is relatively low (8 per cell) when that of C7H8 is 36 per cell. In addition, the density distributions indicates that different contaminations are preferentially adsorbed inside the super-cage of NaY zeolite. Overall, this work analyzes the adsorption mechanism of NaY zeolite on typical contaminations, and can provide basic insights for the development of zeolite molecular adsorber coating with high adsorption capacity.
With the rapid development of industry, copper metal pollution in wastewater discharged from related manufacturing fields has become increasingly serious.Meanwhile, demand for copper metal resources in the field of catalysis is increasing. In this study, low-cost modified calcium silicate hydrate (PCSH) was prepared using fly ash and modifier polyethyleneimine (PEI) for the adsorption of heavy metal copper ions(Cu(II)) in aqueous solution, and then the Cu(II), immobilized on the surface, was further treated with alkali to form copper-based active material for catalytic degradation of organic pollutants. Compared with unmodified sample (CSH), the maximum adsorption capacity of PCSH for Cu(II) was increased by 100% with the maximum of 588 mg/g. The main reason was that the addition of PEI facilitated formation of larger specific surface area, excellent pore structure and strong complexation between Cu(II) and -NH2. The copper-based catalysts, which obtained from PCSH exhibiting spindle-shaped porous morphology, could catalyze the oxidative degradation of rhodamine B (RhB) by activating potassium peroxymonosulfate (PMS) and the reduction of 4-nitrophenol (4-NP) by activating sodium borohydride (NaBH4), with rate constants of 0.7135/min (pH (7.0±0.3); [RhB]= 20 mg/L; [PMS]= 0.12 g/L; [catalyst]= 0.8 g/L) and 11.47×10-3/s (pH (11.0±0.3); [4-NP]= 10-4 mol/L; [NaBH4]= 5×10-3 mol/L; [catalyst]= 0.167 g/L), respectively, about 20 and 19 times as large as those of CSH catalyst system, respectively. The present work achieves the reuse of copper element in aqueous solution by using solid waste fly ash, which provides new insights into effective treatment and utilization of pollutants in water.
Photocatalysis has received extensive attention due to its advantages of mild reaction conditions and direct conversion of solar energy to chemical energy. Improving the solar absorption range and reducing the recombination of photo-generated “electron-hole” pairs are the hot topics in the field of photocatalysis. In this work, the amorphous TiO2 nanotube arrays (TiO2NTs) were prepared by anodic oxidation, and indium-tin (In-Sn) alloy was pressed into the amorphous TiO2NTs by a mechanical hydraulic method to make In9.45Sn1/TiO2NTs, then the In9.45Sn1/TiO2NTs were annealed in air to obtain indium tin oxide (ITO)/TiO2NTs. The photocatalytic properties of the obtained TiO2NTs, In9.45Sn1/TiO2NTs and ITO/TiO2NTs on the removal of methylene blue in aqueous solution were studied and compared. After 180 min visible light irradiation, the degradation efficiency of the ITO/TiO2NTs reaches 96.14%. The applying UV-Vis diffuse reflectance spectroscopy (UV-Vis DRS) to explore the optical adsorption abilities of the samples shows the strongest absorbance of ITO/TiO2NTs. Combining the results of transient photocurrent responses, photocurrent density-potential, electrochemical impedance spectroscopy, and Mott-Schottky plots, the ITO/TiO2NTs have higher charge transfer capability and donor density than do other samples, which can reduce the recombination of holes and electrons, thus improving the visible-light catalytic performance. After five cycles, the degradation rate of the ITO/TiO2NTs still maintains 90.28%. Results of free radicals trapping experiments reveal that •O2- and •OH are the main active substances for the photocatalytic degradation.
Drinking water contaminated with arsenic for a long time will inevitably lead to serious human health problems. Suitable adsorbent for arsenic removal from water is an urgent but a challenging task. In this study, halloysite nanotubes-supported ZrO2 (ZrO2/HNT), a novel and efficient arsenate adsorbent, was prepared using a straightforward hydrothermal method. Its morphology and structure were characterized. ZrO2 nanoparticles with monoclinic phase were well dispersed on the outer walls of halloysite nanotubes. And the ZrO2/HNT could effectively remove As(V), achieving adsorption equilibrium within 30 min. The saturation As(V) adsorption capacity was 27.46 mg/g at 25 ℃. Its adsorption capacity decreased with the increase of the solution’s pH. Coexistent ions (except phosphate) showed little effect on adsorption performance of As(V). The As(V) adsorption kinetics fitted well with pseudo-second-order modeland the As(V) removal processes were endothermic which was verified as chemisorption reactions based on calculation of Gibbs free energy and Dubinin-Radushkevich (D-R) isotherm model. Fourier transform infrared (FT-IR) and X-ray photoelectron spectrometer (XPS) study indicated that the As(V) adsorption processes mainly proceeded through ligand exchange between As(V) and hydroxyl groups on the surface of ZrO2 in the ZrO2/HNT and formation of inner-sphere surface complexes. This study suggest that the as-synthesized ZrO2/ HNT is a potential candidate for practical applications of As(V) removal from water.
Ti3C2Tx MXene is a potential adsorbent of heavy metal ions due to its two-dimensional layered structure and abundant surface functional groups. However, it has disadvantages of limited layer spacing and poor stability in aqueous solution. Here, the modification strategy of Ti3C2Tx was explored to improve its chemical stability and ion adsorption capacity among which Fe3O4-Ti3C2Tx(FeMX) adsorbent with different doping amounts of Fe3O4 were prepared by one-step hydrothermal method. The results showed that the maximum theoretical Pb(II) adsorption capacity of FeMX adsorbent could reach 210.54 mg/g. Its adsorption mechanism was further revealed that Fe3O4 nanoparticles were evenly dispersed and intercalated between Ti3C2Tx nanosheets, which effectively increased specific surface area and layer spacing of Ti3C2Tx nanosheets, leading to improving Pb(II) removal ability. Therefore, this study provides a promising route for developing MXene matrix composites with excellent heavy metal ion adsorption properties.
Broad application of nuclear energy has resulted in the release of radionuclides such as uranium [U(VI)], into the environment, and its potential toxic and irreversible effects on the environment are among the paramount issues in nuclear energy use. Graphite carbon nitride (g-C3N4) is a kind of non-metallic material with the triazine structure. In recent years, the reduction of U(VI) to insoluble U(IV) by g-C3N4 photocatalysis has become a major research focus on the area of radioactive pollutants. In this work, a metal-organic framework (MOF) material containing cobalt metal was used as a self-sacrificial template. Through simple thermal copolymerization, the Co-Nx coordination was successfully incorporated into g-C3N4 to synthesize the CoNx/g-C3N4 photocatalyst. The effects of the morphology, structure, and photoelectric properties of CoNx/g-C3N4 on the photocatalytic reduction of U(VI) were investigated using macroscopic batch experiments. The results showed that the introduction of Co effectively broadened the absorption range of g-C3N4 to visible light, inhibited recombination of the photogenerated electrons and holes, and facilitated the reduction of U(VI). Under irradiation in visible light for 45 min, pH 5.0 and solid-liquid ratio of 1.0 g/L, the photocatalytic reduction of a standard 50 mg/L U(VI) solution reached 100% by CoNx/g-C3N4(w(Co-MOFs) : w(g-C3N4)=1 : 1). Furthermore, the photocatalytic mechanism of CoNx/g-C3N4 was investigated through capture experiments. In summary, the CoNx/g-C3N4 composite exhibits excellent optical performance, has simple operation, is eco-friendly, and has a significant photocatalytic effect on U(VI) in radioactive wastewater. This work also provides design strategy and technical reference for applying g-C3N4 materials to treat radioactive wastewater.
Removal of uranium (VI) from uranium (VI) containing waste water is urgently needed with the global nuclear energy exploitation. The present work completed synthesis of fluorapatite and removal of uranium (VI). Fluorapatite was synthesized using calcium fluoride, calcium pyrophosphate and calcium hydroxide as the raw materials. The fluorapatite before and after adsorption of uranium (VI) was characterized. The experimental results show that, at condition of 308 K, pH=3, solid-liquid ratio of 0.12 g/L, equilibrium time of 120 min and initial uranyl ion concentration of 100 mg/L, the adsorption capacity of uranium (VI) by fluorapatite reaches 655.17 mg/g. Adsorption process of uranium (VI) by fluorapatite is in accordance with the pseudo-second-order kinetics and Langmuir isotherm adsorption model. Adsorption of uranium (VI) by fluorapatite is a spontaneous and endothermic reaction. The removal of uranium (VI) by fluorapatite is ascribed to surface mineralization. After uranium (VI) is absorbed, a new phase of meta-autunite [Ca(UO2)2(PO4)2·6H2O] is generated on the surface of fluorapatite. The meta-autunite can maintain high stability in the pH≥3 aqueous solution. Above results indicate that fluorapatite can be used as a promising mineralizer for purification and solidification of uranium (VI) containing waste water.