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.

TiO₂ nanomaterials are widely used photocatalysts due to high photocatalytic activity, good chemical stability, low cost, and nontoxicity. However, its lower photon utilization efficiency is still limited by larger bandgap width and higher recombination rate between photon and hole. In this study, two-dimensional TiO₂ nanosheets were synthesized via microetching, which were then inserted by ruthenium atoms to form an efficient photocatalyst Ru@TiO₂ with sandwich structure. The surface morphology, electronic structure, photoelectric properties, and photocatalytic degradation performance of tetracycline hydrochloride of Ru@TiO₂ sandwich structure were investigated using different measurements. Results indicated that the material’s photoresponse range extended from UV to visible- near-infrared regions, improving photon absorption and carrier separation efficiency while enhancing photocatalytic activity. Under simulated sunlight irradiation (AM 1.5 G, 100 mW·cm^-2) for 80 min, sandwich structured Ru@TiO₂ efficient photocatalyst exhibited superior degradation performance on tetracycline hydrochloride with a degradation efficiency up to 91.91%. This work offers an effective way for the construction of efficient TiO₂ based photocatalysts.

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⁺.

Ti₃C₂T_x 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 Ti₃C₂T_x was explored to improve its chemical stability and ion adsorption capacity among which Fe₃O₄-Ti₃C₂T_x(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 Ti₃C₂T_x nanosheets, which effectively increased specific surface area and layer spacing of Ti₃C₂T_x 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.

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.

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 In_9.45Sn₁/TiO₂NTs, then the In_9.45Sn₁/TiO₂NTs were annealed in air to obtain indium tin oxide (ITO)/TiO₂NTs. The photocatalytic properties of the obtained TiO₂NTs, In_9.45Sn₁/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.

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.

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.

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.

Fe@zeolite materials are widely applied in the production of ·OH by catalyzing Fenton-like reactions for degradation of recalcitrant organic pollutants due to their comprehensive sources, simple preparation and low environmental impact. However, the high cost of Fe@zeolite synthesis and the lack of Fe²⁺ regeneration strategy are serious issues that limit the application of Fe@zeolite as a Fenton-like catalyst in industrial-scale systems. In this study, the ash generated from activated sludge incineration treatment was utilized as raw material to selective recover Si, Al and Fe, preparing Fe²⁺-sodalite (FSD) material. Consequently, it was used as a Fenton-like catalyst to activate peroxyacetic acid (PAA) for the degradation of methylene blue (MB) in wastewater. Results indicated thatFSD was capable of effectively catalyzing PAA to generate various active oxygen species such as ·OH, ¹O₂ and R-O· in a wide pH range, thereby degrading MB through hydroxylation and sulfonation pathways. MB can be completely removed during 20 min under optimized conditions of 0.3 mmol/L PAA and 0.3 g/L FSD prepared with 0.5 mol/L Fe²⁺. In addition, the reductive S species in FSD can maintain its catalytical activity by enhancing Fe²⁺ regeneration, and the FSD/PAA system has been proven to be effective in the degradation of various organic pollutants under practical and complex environmental conditions.

Activated carbon's porous nature and high specific surface area make it an effective tool for adsobing waste gas containing styrene. However, the mechanism by which oxygen-containing functional groups adsorb weak-polar styrene remains unclear. This study described the preparation of the modified activated carbon materials AC-S and AC-N using the acid leaching method. The pore structure and specific surface area of modified activated carbon, the evolution of oxygen-containing functional groups, and their impact on the styrene-adsorbing performance were investigated. The results demonstrated that acid modification significantly improved the styrene-adsorbing capacity of activated carbon. Physical and chemical adsorption impacted both modified and unmodified activated carbon materials, as determined by the adsorption kinetics studies and isotherm fitting analyses. Monolayer adsorption was more likely to occur on modified activated carbon. HNO₃-modified activated carbon (AC-N) maintained its effective styrene adsorption pore size range. The increasing number of oxygen-containing functional groups on the surface improved the styrene adsorption performance of AC-N. Study of oxygen-containing functional groups on the surface revealed that lactone group was a key factor in improving the modified activated carbon's ability to adsorb styrene. Density functional theory (DFT) calculations showed that lactone group on AC-N strongly interacted with the vinyl group in styrene, thereby enhancing the styrene adsorption performance of modified activated carbon.

Preparation of alkali metal doped g-C₃N₄ materials is an important branch in the research of g-C₃N₄ semiconductor photocatalytic materials. However, there is still lack of study on g-C₃N₄ materials revealing mechanisms in photosensitizer-assisted photocatalytic degradation. In this study, Na⁺ doped g-C₃N₄ photocatalysts (Na⁺/g-C₃N₄) were prepared using solution synthesis, calcination, and solvothermal reaction methods.The doped position of Na⁺ in g-C₃N₄ and photoelectric performance were determined. The changes of morphological, specific surface area, and pore size of Na⁺/g-C₃N₄ materials were analyzed by scanning electron microscopy, N₂ adsorption and desorption experiments. In Na⁺/g-C₃N₄ materials, the Na⁺ loaded in a cyclic structure composed of three heptazine structural units, coordinating with N atoms. Na⁺/g-C₃N₄ changed the adsorption performance of g-C₃N₄, altered its bandgap width and position of conduction (valence) band, and increased its separation rate of photogenerated electrons and holes and charge transport rate of the material by affecting the π-conjugated system of g-C₃N₄. During the solvothermal reaction process for synthesis of Na⁺/g-C₃N₄, strong hydrolysis caused decomposition of unstable structures of g-C₃N₄ while the C-O^- bonds were formed at the edge of g-C₃N₄. The physical and chemical adsorption sites for methylene blue (MB) of Na⁺/g-C₃N₄ materials are confirmed by π-conjugated system and C-O^- bonds of Na⁺/g-C₃N₄, by which Na⁺/g-C₃N₄ materials can adsorb MB up to 93.25%, in contrast to the g-C₃N₄ materials’ adsorbtion only up to 24.50%. Under visible light irradiation, due to their strong adsorption capacity and photosensitivity to MB, Na⁺/g-C₃N₄ materials have constructed a unique photosensitive- photocatalytic degradation system with MB. MB not only acts as the photosensitizer for self degradation but also collaborates with Na⁺/g-C₃N₄ materials for photocatalytic degradation. At pH 6.0, the maximum degradation rate of MB is up to 96.40% in the photosensitive-photocatalytic system constructed with MB and Na⁺/g-C₃N₄ samples.

Construction of heterojunction can effectively suppress the swift recombination of photogenerated electrons and holes in photocatalyst. In this study, a II/Z-type Bi₂MoO₆/Ag₂O/Bi₂O₃ heterojunction photocatalyst was synthesized using a solvothermal method combined with calcination. Various techniques were ultilized to examine the composition, morphology and photoelectrochemical properties of the as-prepared materials. The findings revealed that the optimal composition of the composite material was 25%ABOBM (with a mass ratio of Ag₂O/Bi₂O₃ and Bi₂MoO₆ of 1 : 4). Under visible light irradiation, the degradation efficiency of tetracycline (TC) by 25%ABOBM reached 85.6%, which was significantly higher than that of Ag₂O/Bi₂O₃ and Bi₂MoO₆, and maintained its good stability after three cycles of experiments. The enhanced photocatalytic performance of 25%ABOBM is attributed to the formation of heterojunctions and the unique morphologies among Ag₂O, Bi₂O₃ and Bi₂MoO₆. Both h⁺ and ·O₂^- are significant contributors, while ·OH and ¹O₂ have secondary roles in the degradation process of TC, as indicated by free radical capture experiment and electron paramagnetic resonance spectroscopy (EPR). Furthermore, the related photocatalytic mechanisms were explored, and the potential degradation pathways of TC were analyzed using liquid chromatography-mass spectrometry (LC-MS). This study offers a novel approach to the preparation of photocatalysts with dual heterojunctions and demonstrates their application in the degrading organic pollutants.

Photocatalysis is widely employed to treat emerging pollutants in water, due to its well-organized attributes. Self-sensitive carbon nitride (SSCN) represents a novel class of non-metallic photocatalyst that has garnered significant attention for its distinctive properties in contrast with traditional graphitic carbon nitride (g-C₃N₄). However, their visible-light photodegradation effect remained still to be enhanced. Here, SiO₂ microspheres were initially synthesized by the Stöber method, followed by the preparation of SiO₂/SSCN composites through an in-situ hydrothermal process. Their microstructure, phase structure, and photoelectric properties were systematically investigated using a combination of characterization techniques. It is discovered that the SiO₂ within the composites effectively disperses in the SSCN. The obtained composite material was then applied to photocatalytic degradation of antibiotic pollutants in water, exhibiting enhanced degradation activity, which was closely correlated with the quantity of SiO₂. At mass ratio of SiO₂ to SSCN of 0.04 : 1, the composite achieved optimal photocatalytic activity and demonstrated good stability. After irradiation for 60 min, 42% of tetracycline hydrochloride was degraded, and the photocatalytic degradation efficiency remained at 38% after 5 cycles. Furthermore, incorporation of the SiO₂ component offers supplementary sites for the dispersion of SSCN, mitigating serious agglomeration phenomenon of SSCN. This facilitates the rapid decomposition of 1,3,5-triazine oligomers (TBO) on the surface of SSCN under light irradiation, and the optimizing content of TBO on surface active sites. Consequently, utilization efficiency of visible light on SSCN is significantly improved, and a higher separation rate of photogenerated electron-hole pairs is simultaneously observed. These attributes culminate in significantly improved photocatalytic activity for the degradation of tetracycline hydrochloride on SSCN under visible light irradiation. Above advantages may position the as-synthesized SiO₂ dispersed SSCN as prospective candidate for practical application. Therefore, this research offers a novel route for enhancing the photocatalytic activity and stability of catalysts.