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Contact-electro-catalysis (CEC) is a green catalytic technology that reduces emissions and purifies the environment via contact electrification (CE) at the solid–liquid (S–L) interface to generate reactive oxygen species. However, CEC technology faces limitations under natural and industrial conditions and urgently needs to be developed to promote self-powered or low-cost chemical reactions using environmental energy. A low energy-conversion rate under complex natural or industrial conditions is the key limiting factor for large-scale applications. In this review, CEC under various natural and industrial conditions is discussed. First, the competitive relation between electron transfer and ion transfer in CE is proposed, wherein the CE mechanism details are compared to determine the effect on CEC. Additionally, strategies for promoting S–L electron transfer and controlling ion transfer are systematically analyzed using the condition factors of the solid catalyst, water phase, and external environment, such as functional groups, ions in the liquid, and temperature. Finally, the challenges associated with CEC technology in engineering implementation are summarized. This review aims to provide insight into the competitive relation between electron and ion transfer in S–L CE for CEC and provides new ideas for the engineering of CEC technology under complex natural and industrial conditions. [ABSTRACT FROM AUTHOR]

Nanozymes are next-generation of nanomaterials with enzyme-like activities. In particular, nanozymes with peroxidase (POD)-like activity have been utilized in various fields, including antibacterial, detection, degradation, etc. However, their extensive applications were limited by their low catalytic activity currently. Herein, we have presented a composite nanozyme based on attapulgite (ATP) (Fe-ATP-MoS2 (FAM)), which exhibited enhanced POD-like activity (185.33 U·mg−1), 4.25 times higher than that of Fe-MoS2 (FM) (43.63 U·mg−1). The density functional theory (DFT) calculations indicated that the addition of ATP increased the electron density of metal centers (Mo and Fe). More importantly, Michaelis–Menten kinetics revealed that the introduction of ATP significantly enhanced the binding affinities of substrates through the pores of ATP, forming a highly concentrated substrate microenvironment and thus promoting its POD-like activity. Additionally, from molecular size and kinetic analysis, we proposed that the changes in substrate size before and after oxidation also significantly affected its Michaelis-constant (Km) value. Furthermore, we utilized FAM in the applications of highly effective antibacterial application and sensitive detection of glutathione (GSH). In conclusion, this work provides a novel approach for designing a highly efficient nanozyme based on natural mineral composites. [ABSTRACT FROM AUTHOR]

Degradable triboelectric nanogenerators (TENGs), which use degradable polymer materials as the friction layer, have become the optimal choice in the field of electronic skin, wearable devices, and other new energy sources owing to their biocompatibility and degradability. However, the inferior output performance of degradable TENGs hinders their practical applications. Various strategies, such as modifications and surface optimization of the friction material, have been employed to deal with this challenge. In this review, we introduce the methods used for composition modifications and structural optimization for each type of degradable polymer used in TENGs and also discuss their other functions, such as degradability, antimicrobial properties, and biocompatibility. We summarize typical cases and the characteristics of each type of degradable polymer. Finally, we also discuss the challenges and future prospects for enhancing the properties of degradable TENGs, including the options for degradable polymers, their processability, and the bionic approach to materials design. We anticipate that this review will provide guidance for and assistance in constructing high-performance TENGs based on degradable polymers. [ABSTRACT FROM AUTHOR]

Significant progress has been made in using triboelectric nanogenerators (TENGs) to harvest sustainable energy from wind, waves, human activities, and water droplets. Natural materials, which are non-synthetic and have the advantages of being low-cost, environmentally friendly, biodegradable, and partially biocompatible, can be used to prepare green TENGs. In this review, the latest advances made in natural-materials-based TENGs are summarized. The triboelectric mechanisms and properties of natural-materials-based TENGs derived from animals, plants, humans, microorganisms, and minerals are discussed. The output performance, features, and applications of the natural materials used to construct the tribopositive and tribonegative layers of TENGs are discussed. Moreover, the triboelectric sequence of the natural materials is summarized to compare their ability to gain or lose charge in the process of friction. Finally, the challenges facing natural-materials-based TENGs, such as complex processing, short service life, lack of stability, few tribonegative materials, and low power density, are listed. It is thus anticipated that this review will encourage the use of natural materials to manufacture eco-friendly TENGs that have broad application prospects in the field of energy conversion. [ABSTRACT FROM AUTHOR]

Tribocatalysis is an emerging technology that can convert mechanical energy into chemical energy to degrade organic pollutants. The two widely used tribocatalysis mechanisms are the electron transfer and transition mechanisms. Currently, there is no definitive criterion to determine which mechanism is best employed for proper implementation in a tribocatalysis reaction. In this review, research that compares the two mechanisms through their electronic structures as criteria for selection is discussed. The factors influencing the tribocatalysis performance as well as criteria for tribocatalysis mechanism selection are the surface state, energy band structure, and force. Finally, the proposed standard method to analyze the electronic state, relation between the catalyst and H2O (O2), energy band bending theory, and charge preservation for tribocatalysis must be explored for tribocatalysis mechanism development. This review seeks to elicit meaningful discussion for distinguishing the unique characteristics of the two existing mechanisms and understanding the details of tribocatalysis mechanisms. [ABSTRACT FROM AUTHOR]

Piezocatalysis can be used to harvest widely existing and renewable mechanical vibrations in the environment to convert mechanical energy into chemical energy, which is employed in various important applications, and typically, the polyvinylidene fluoride (PVDF)/graphene composite piezocatalyst is used because of its recyclability, flexibility, and easy preparation. However, its poor piezocatalytic performance, primarily attributed to the wrapped graphene in the PVDF matrix that prevents the generated charges from fully accessing pollutants, remains a challenge. Herein, we use phase conversion and the "self-assembly strategy" to prepare a sandwich film called PVDF-hexafluoropropylene@reduced graphene oxide (PVDF-HFP@rGO) with PVDF-HFP as the interlayer and rGO as the outer layer to fully expose rGO. Under magnetic stirring at 600 rpm, the degradation efficiency of PVDF-HFP@rGO toward methylene blue reaches ∼98% within 60 min, higher than those of the traditional composite film (∼75%) and pure PVDF-HFP film (∼8.0%). The charge supply by rGO, piezoelectric field provision by PVDF-HFP, and advantage of the sandwich structure are verified through contrast experiments under different conditions such as changing rGO band structures, varying PVDF-HFP interlayer thicknesses, and using different layer structures, respectively. Therefore, the enhanced piezocatalytic performance of the sandwich structure provides new insights into the structural design of high-performance PVDF/graphene composite piezocatalysts. [ABSTRACT FROM AUTHOR]

Fiber composite materials with filler–matrix friction between fibers can produce triboelectric signals realizing endogenous triboelectric nanogenerators (TENGs). Endogenous TENGs are easy to package and do not require controlled distance as piezoelectric nanogenerators (PENGs) do, but without piezoelectric materials. However, limited studies have been conducted on the design and control of the filler content and distribution in fibers to improve the electricity generation of endogenous TENGs, which is significant for the evolution as a replacement for PENGs. In this study, an endogenous TENG was prepared using a polylactic acid (PLA) composite fiber film and MXene as the matrix and filler, respectively. The generated open-circuit voltage, short-circuit current, and charge increase when PLA–MXene contacts are introduced between the fibers, reaching the highest values of 16 V, 1.2 μA, and 7 nC, respectively, in the case of 1 wt% MXene/PLA (1 wt% PMX). Then, a blend film (B-M film) was designed to optimize the MXene distribution to further increase the number of PLA–MXene contacts and the B-M film with 1 wt% MXene shows a higher output power of 4.55 μW cm−2 than that with 1 wt% PMX (1.23 μW cm−2). This study reveals the effects of the filler content and distribution on the electricity generation of endogenous TENGs based on composite fiber films, and the employed blending strategy provides a new idea for improving their output performance. [ABSTRACT FROM AUTHOR]

The molecularly selective catalysis in enzyme is central to life. However, their functioning mechanism remains elusive. We propose here that the synergistic effects from (i) effective orbital hybridizing and energy gap decreasing via chelating on single Zr atom as the catalytic center, (ii) selective supramolecular encapsulation in the cage, and (iii) piezoelectrical field motivation are able to achieve the enzyme‐mimetic molecular selective high performance catalysis. Metal–organic polyhedra (MOPs) are added into a piezoelectrical polymer matrix to achieve the composite structure where ultrasonic treatment motivates redox reactions in the MOP‐guest complex. Encapsulated and chelated guest such as Rhodamine B (RhB) is effectively converted with ratios higher than 90 % after 100 min. In comparison, molecules inefficient in either cage encapsulation or chelating with the Zr center can not be converted. This study first proposes a synergistic plot for enzyme‐mimetic catalyst realization and is expected to inspire new mentality in efficient catalyst designing. [ABSTRACT FROM AUTHOR]

Polymer fiber filters, with their high surface area, low cost, and easy large‐scale manufacturing, are widely used in air purification. These filters have been combined with various types of functional nanoparticles to endow them with electrostatic adsorption, photocatalysis, electrocatalysis, photoelectrocatalysis, or antibacterial properties, and improve their filtering performance. In this study, a summary of the research on single polymer and polymer composite filters for highly efficient air purification is presented. In single polymer filters, polar groups in the polymer chains, a rich porous structure, and electret process improve their removal capability. In polymer composite filters, metal–organic frameworks, porous particles, and electret materials as fillers improve the physical adsorption of the materials, while the use of photocatalysts, electrocatalysts, photoelectrocatalysts, and antibacterial agents as functional fillers endows the filters with additional chemical reactions for the complete degradation of gas and microorganism pollutants. Finally, the challenges that remain in the development of polymer filters for use in air purification are also discussed in terms of material type and fabrication technology. It is expected that polymer filters with tunable surface properties and multifunctions can realize highly efficient air purification with low energy consumption. [ABSTRACT FROM AUTHOR]

Natural nanominerals (NNMs) are progressively deposited during earth's formation. They have shown a broad range of applications from industrial catalysis, environmental treatment, and earth science to pharmaceutics due to their unique nanostructures and characteristics. Here, we first report that NNMs have intrinsic enzyme-like properties and show good biocompatibility. First, we characterized the morphology and structure of the six most representative NNMs including sepiolite, attapulgite, halloysite, montmorillonite, kaolinite, and diatomite by SEM, TEM, and XRD. Then, we quantitatively tested their peroxidase- (POD-), catalase- (CAT-), oxidase- (OXD-), and superoxide dismutase- (SOD-) like activities. The results indicate that different kinds of NNMs show varying degrees of POD-like, CAT-like, and SOD-like activities and minor OXD-like activity. Finally, we tested their cytotoxicity and found that the selected representative NNMs have no or less influence on cell viability, showing high biosafety. At present, NNMs have been widely used, mostly focusing on the physical and chemical properties, such as luminescence and conductivity. Our work promotes the understanding of NNMs, providing a new direction for the better application of NNMs. [ABSTRACT FROM AUTHOR]

Abstract Promoting semiconductor photocatalytic power is expected to address global energetic and environmental challenges. Piezophotocatalysis is an effective strategy to achieve superior catalytic performance, however, realistic applications of previous piezophotocatalysts have been hampered by the ultrasonication conditions that they require. We propose a new material design to achieve superior piezophotocatalysis by combining semiconductors with a self-powered energy cushion that is driven by gentle mechanical disturbances such as water flows. The energy cushion consists of a porous composite graphene-piezoelectric polymeric film which combines piezoelectric and dielectric power generation and stores the electricity in situ. This energy cushion results in a large and prolonged electric field in response to gentle mechanical disturbances. The electric field, in turn, enhances photocatalytic performances of TiO 2 , BiOI, or CdS by 300%, 21%, and 400%, respectively. In addition, this new material does not consume additional energy when promoting the catalytic performance of semiconductors. We expect the concept of combining these semiconductors with such an energy cushion to lead photocatalysis a step closer to realistic future applications. Graphical abstract Remarkably enhanced catalytic efficiency of semiconductor particles are realized by mounting them onto a energetic cushion, which is a self-powered piezoelectric-dielectric rGO-F/PVDF-HFP composite polymeric porous film. The film effectively converts the mechanical disturbances of water flow into electric field which in turn enhanced semiconductor catalytic capabilities. fx1 Highlights • The films achieved both generation and energy storage properties. • The porous structure enabled the film's high responsivity to mechanical disturbance. • The porous film promoted photocatalytic capabilities of the semiconductors. [ABSTRACT FROM AUTHOR]

Because of the large amounts of iron and aluminum in red mud, which is a by-product of the alumina industry, aluminum and iron can be extracted by HCl or H2SO4 to produce inorganic flocculants. However, residues produced by acid leaching pose environmental problems. In this study, a slow-release mineral fertilizer K2MgSi3O8 is prepared at 1,000°C for 2 h by sintering the flocculant by-product based on red mud. The main mineral in the fertilizer is K2MgSi3O8, with an irregular blocky morphology. In distilled water, 0.50 mol/L HCl, and 20 g/L citric acid, the dissolution rates of K2O are 13.13%, 96.36%, and 81.46% and those of MgO are 2.03%, 70.94%, and 66.03%, respectively. Cumulative release values of K2O and MgO are 6.98% and 0.01% on the first day and 56.12% and 1.70% after 28 days, and the slow-release rates satisfy the Chinese standard for slow-release fertilizers. Hence, the mineral fertilizer K2MgSi3O8 based on the by-product of red mud is a potential slow-release fertilizer. [ABSTRACT FROM AUTHOR]

Recycling of iron ore tailings (IOT) which are by‐products of iron ore processing has attracted attention but there have been few studies on their use as fertilizers. In this study, slow‐release silicon fertilizers are prepared from iron tailings by solid‐phase sintering and characterized by X‐ray diffraction (XRD) and scanning electron microscopy (SEM). The solubility results acquired from the optimal sample (Si‐IOT) indicate that the available SiO2 is 20.77% and that of available K2O is 18.43% in 0.50 mol L−1 HCl. For 10 g of Si‐IOT in 200 mL of distilled water at 25°C, the cumulative release of K2O is 4.32% in the first day and 19.4% in 28 days and that of SiO2 is 2.12% in the first day and 16.30% in 28 days. The performance satisfies the Chinese national standard for slow‐release fertilizers and Chinese agricultural standard for silicon fertilizers. The results obtained from Si‐IOT pertaining to release of heavy metals indicate that heavy metals will not affect the quality of the crops and pakchoi growth is improved. Hence, they are potential raw materials for slow‐release silicon fertilizers. © 2017 American Institute of Chemical Engineers Environ Prog, 37: 1011–1019, 2018 [ABSTRACT FROM AUTHOR]

Red mud and carbide slag which are industrial waste materials from alumina and chlor‐alkali plants pose environmental risks due to the large production volume. However, reutilization has been limited due to their composition and structure and the large alkali concentration in red mud has hampered utilization of red mud. At the same time, flue gas produced during the process of coal firing is a major environmental threat causing greenhouse effects and fog haze. In this work, alkalis (Na2O) in red mud were released by the alkali and acid methods and carbide slags and flue gas were utilized to remove alkalis from red mud. The effects of the reaction time, temperature, and solid‐to‐liquid ratio on dealkalization of red mud by carbide slag were studied. Flame absorption and X‐ray diffraction were employed to monitor the changes in the red mud before and after dealkalization. Under the optimal conditions, the residual Na2O amount in the red mud after dealkalization using the carbide slag diminished to less than 3 wt%, whereas that of Na2O dropped to less than 2 wt% using flue gas. The pH of the suspension is determined by the acid method. The hydroxysodalite (Na8Al6Si6O24(OH)2) structure in the initial red mud was destroyed and soluble sodium salts formed in the suspension can be easily replaced by carbide slag or flue gas reducing Na2O. [ABSTRACT FROM AUTHOR]

As a kind of industry dust and one source of PM2.5, carbon ash, mainly composed of amorphous carbon and ZnO, is urgently to be utilized. In this work, carbon ash and acid treated carbon ash were used as novel conductive filler to prepare high-k composites with high density polyethylene (HDPE). When the content of carbon ash was up to 20 wt %, carbon ash/HDPE composite possessed of a high dielectric constant of 83 at l000 Hz, which was about 36 times of pure HDPE. Using acid treated carbon ash as filler, the composite would have an enhanced dielectric constant of 458, when the filler content was 20 wt %. This was caused by the different conductivity of fillers before and after treated by acid. Besides, 3-aminopropyltriethoxysilane was employed to decrease the dielectric loss of the composites through modifying those fillers. The results showed that carbon ash was good candidate to prepare high-k composites. © 2017 American Institute of Chemical Engineers Environ Prog, 36: 1719-1724, 2017 [ABSTRACT FROM AUTHOR]

A low-cost organolayered double hydroxide adsorbent prepared under alkali conditions with red mud (waste tailings from alumina production) and brucite is modified by anionic surfactant, sodium dodecyl benzene sulfonate (SDBS), by ion exchange to produce a layered double hydroxide adsorbent (LDH-SDBS). LDH-SDBS was used to treat 2,4,6-trinitrotoluene (TNT) red water that had high toxicity, contained persistent compounds, and had a high chemical oxygen demand (COD). Removal efficiency reached 46% at 20-fold dilution (COD, 4024 mg/L) and kinetics showed that adsorption processes followed a pseudo-second-order model. Negative ΔG and positive ΔH indicated adsorption was spontaneous and endothermic and Gas Chromatography-Mass Spectrometer (GC/MS) revealed that amounts of organic compounds in TNT red water were reduced significantly. [ABSTRACT FROM AUTHOR]

Phosphate removal was important for wastewater treatment, and adsorption was an efficient treatment process. In this study, the layered double hydroxide adsorbent (BR-LDH), which was prepared under alkali conditions using industrial residues boron mud and red mud, was used to adsorb the phosphate. The prepared BR-LDH was characterised by X-ray diffraction, Scanning electron microscopy, Energy-dispersive X-ray spectroscopy, and Thermo-gravimetric-differential thermal analysis. Adsorption experiments were carried out as a function of dosage, contact time, temperature and initial pH of phosphate solution. The removal ratio of phosphate onto OBR-LDH reached 93%. The adsorption data showed a good compliance with the pseudo-second-order kinetic model. In addition, the mineral composition, the functional groups, the valence of elements and zeta potentials of OBR-LDH before and after adsorption were used to analyse the adsorption mechanism. The result of real wastewater suggested that OBR-LDH was excellent adsorbent for phosphorus removal from actual wastewater. [ABSTRACT FROM AUTHOR]