Water Adsorption Capacity Research Articles

Fatigue resistance, re-usable and biodegradable sponge materials from plant protein with rapid water adsorption capacity for microplastics removal

Microplastics in water environment has become a particular concern to global ecosystems and attracted wide attention in recent years. Sponge materials have been developed for efficient removal of various water pollutants including organic dyes. However, such sponge materials for microplastics removal has seldom been explored. Herein, a natural and biodegradable sponge material with high mechanical properties was fabricated from plant protein through chemical crosslinking with a compressive strength of 176 kPa and Young’s modulus of 60.1 kPa. After 100 compression cycles at compressive strain of 70%, the mechanical properties of sponge still remained up to 90%, which shows excellent fatigue-resistance close to commercial polyurethan sponges. The abundant active side chains on amino acid residues have provided the protein sponge good capacity to adsorb microplastics (removal efficiency up to 81.2%) at pH range pH 6–9 with an initial microplastic concentration of 1 mg L−1, which presents the pH and MPs concentration of water systems. The adsorption kinetic study suggested that the hydrophobic interactions and the intra-particle diffusion were driving the adsorption process. The sponge possessed highly interconnected porous structure (83%), thus showed fast adsorption ability to microplastics with 38% adsorbed onto the sponge within 10 s. The entrapped water can be released from the sponge simply by squeezing for cyclic use and the fast adsorption ability was still maintained after 20 cycles. In addition, the sponge demonstrated good be biodegradability, thus avoiding secondary contamination when applied for water treatment. This research has provided new thinking of sponge material fabrication from sustainable plant protein raw materials, and the sponge showed potential to be used as a biodegradable material for microplastic removal.

Thermal stability evaluation of selected zeolites for sustainable thermochemical energy storage

ABSTRACT In recent times, the thermochemical energy storage (TCES) method is gaining prominence due to its high energy storage density and minimal heat losses compared to the conventional thermal energy storage (TES) methods. This paper presents the cyclability behavior of selected zeolites for the TCES applications. The zeolites were subjected to sequential desorption and adsorption processes for five times using a differential thermogravimetric analyzer (DTG-60H). To investigate their suitability for the commonly available sources of thermal energy (e.g. solar energy, industrial waste heat), the samples were heated up to 150°C. These zeolites were also tested on Brunauer–Emmet–Teller (BET) analyzer for total surface areas and pore volumes, thus to read their sorption behavior. A field emission scanning electron microscope (FESEM) equipped with an energy dispersive X-ray (EDX) analyzer was used to examine the surface morphology and elemental composition of zeolite sorbents before and after the multi-cycle test run. The changes in the mass of a material during a process, either desorption or adsorption, were notably almost the same across the cycles tested, which confirms the cyclability of the materials tested. Amongst the tested materials, Zeolite-NaY and Zeolite-HY exhibited relatively better process enthalpies owing to their active water adsorption capacities. Of the six materials tested, Zeolite-NaY has offered better results and its enthalpies range from 287.5 J g−1 to 348.5 J g−1 for the desorption and from 81 J g−1 to 292.1 J g−1 for the adsorption. A mass gain was noticed for each of the tested materials as they undergo the cooling process, thus affecting water vapor adsorption capacity negatively.

Study of the pilot-scale pan granulation of zeolite-based molecular sieves

This work describes a systematic study of the granulation process of a 5A zeolite into molecular sieves. Initially, a 5A zeolite was synthesized at the pilot scale and subsequently granulated in a core–shell structure using a rotary tilted pan. The effect of water content of the paste, pan rotating velocity and inclination, proportion of zeolite in the core and shell, shell thickness, the type of binding clay, and the calcination temperature were studied. The effect of these variables on the shape, size, water adsorption capacity, and crush resistance of the agglomerates was assessed. According to the results, suitable bead shape and size were obtained at high rotation velocity (59 rpm), low pan inclination (60°) and with 30 wt. % of added water. High content of zeolite in the core and shell provided suitable adsorption capacity, but lower crush resistance. Actigel 208® exhibited better binding performance and the recommended calcination temperature was 873 K.

Evaluation of Sugarcane Agroindustrial Wastes as Substrate in Soilless Cultivation of Tomato (S. lycopersicum Linnaeus): Effect of Substrate Composition on Yield Production

Traditionally, biochar is generally proposed to substitute Canadian Sphagnum peat moss. Sugarcane bagasse, filter press mud and sugarcane bagasse ash were mixed in different ratios and proposed as an alternative to substitute commercial Sphagnum peat moss (SPM) for the soilless cultivation of tomato (S. lycopersicum Linnaeus). The choice of the agroindustrial waste ratio was performed from physical-chemical sample characterization. During vegetable production, an adequate ratio was evaluated based on plant height, substrate pH, number of leaves, yield, and fruit size. The addition of essential macro- and micro-nutrients was performed manually. The results show that as-received materials contain different minerals with a structure that corresponds to the quartz, cristobalite, and feldspar phases. A morphology composed of lamellate structures was observed for sugarcane bagasse, whereas the filter press mud and the sugarcane bagasse ash presented compact agglomerates with a surface area of 1.60, 3.78, and 1.07 m2 g−1, respectively. The properties of each component promote the water adsorption, retention and releasing capacity. Important differences were observed as the quantity of filter press mud increased, but also it is required an amount of sugarcane bagasse above of 18 wt% to reach a superior performance. This work demonstrated that, in adequate quantities, agroindustrial wastes can be used as a soilless substrate for growing tomatoes in greenhouse, reducing their disposal problems.

Adsorption of toluene on silicalite‐1/NaY composites: Influence of NaY pretreatment on hydrophobic properties

The surface hydrophobic modification of NaY zeolite was discussed to improve the adsorption capacity of NaY in VOCs under wet conditions. Silicalite‐1/NaY composites were hydrothermally synthesized in silicalite‐1 precursor solution using NaY (treated with HCl and NaOH) as seed. The textural, porosity, morphology, and adsorption properties of these adsorbents were characterized by X‐ray diffraction, N2 adsorption–desorption, scanning electron microscopy, inductively coupled plasma atomic emission spectroscopy measurements, sequential X‐ray fluorescence spectrometer, and static adsorption experiment of water and dynamic adsorption tests under wet and dry condition. Results showed that the static water adsorption capacity of the composites was greatly reduced compared with pure NaY and the dynamic adsorption of toluene under both wet and dry conditions (relative humidity of 50% and 0%) indicated that the composites possessed high dynamic adsorptive capacity and hydrophobic properties. Among these composites, the sample synthesized by NaY (NaOH pretreatment) displayed the best hydrophobic properties in the competitive adsorption of water and toluene with a toluene adsorption capacity of 56 mg/g.

Moisture Adsorption and Desorption Behavior of Raw Materials for the T-RTM Process

The use of fiber reinforced plastics (FRPs) has significant potential to reduce the weight of components. As regards the sustainability of these components, thermoplastic matrices offer more potential for recycling than thermoset ones. A possible manufacturing process for the production of thermoplastic FRPs is thermoplastic resin transfer molding (T-RTM). In this very moisture-sensitive process, ε-caprolactam in addition to an activator and catalyst polymerizes anionically to polyamide 6 (aPA6). The anionic polymerization of aPA6 is slowed down or even completely blocked by the presence of water. This study analyses the sorption behavior of the matrix, fiber, binder and core materials for the production of anionic polyamide 6 composites, which are processed in the thermoplastic RTM process. Water vapor sorption measurements are used to determine the adsorption and desorption behavior of the materials. The maximum moisture loading of the materials provides information about the water adsorption capacity of the material. This knowledge is crucial for correct handling of the materials to achieve a fast process and good properties of the final product.

Reactive molecular dynamics simulations of hydration shells surrounding spherical TiO2 nanoparticles: implications for proton-transfer reactions.

In many potential applications, nanoparticles are typically in an aqueous medium. This has strong influence on the stability, optical properties and reactivity, in particular for their functionalization. Therefore, the understanding of the chemistry at the interface between the solvent and the nanoparticle is of utmost importance. In this work, we present a comparative ReaxFF reactive molecular dynamics investigation on spherical TiO2 nanoparticles (NSs) of realistic size, with diameters from 2.2 to 4.4 nm, immersed in a large drop of bulk water. After force field validation for its use for a curved anatase TiO2 surface/water interface, we performed several simulations of the TiO2 nanoparticles of increasing size in a water drop. We found that water can be adsorbed jointly in a molecular and dissociative way on the surface. A Langmuir isotherm indicating an adsorption/desorption mechanism of water on the NS is observed. Regarding the dissociative adsorption, atomistic details reveal two different mechanisms, depending on the water concentration around the NS. At low coverage, the first mechanism involves direct dissociation of a single water molecule, whereas, at higher water coverage, the second mechanism is a proton transfer reaction involving two water molecules, also known as Grotthuss-like mechanism. Thermal annealing simulations show that several water molecules remain on the surface in agreement with the experimental reports. The capacity of adsorption is higher for the 2.2 and 3.0 nm NSs than for the 4.4 nm NS. Finally, a comparative investigation with flat surfaces indicates that NSs present a higher water adsorption capacity (undissociated and dissociated) than flat surfaces, which can be rationalized considering that NSs present many more low-coordinated Ti atoms available for water adsorption.

Nitrogen release and re-adsorption dynamics on crop straw residue during straw decomposition in an Alfisol

Returning crop straw to the field not only improves the nitrogen (N) supplying capacity and N retention of soil but also decreases the amount of rural organic waste and prevents air pollution. Therefore, understanding the mechanisms of the N release and re-adsorption dynamics on crop straw residue during straw decomposition in agricultural soil is important, and this understanding can help us strengthen N fertilizer management during the crop growth period. An on-farm incubation experiment was conducted in the Jianghan Plain in Central China under flooded conditions using the nylon mesh bag method. Results showed that the decomposition rate of crop straw was much faster at the beginning of the incubation stage, whereas it was steady during the later stage with no observed differences among the three types of crop straw. After 120 d of incubation, the cumulative decomposition proportion of rice straw, wheat straw and rape straw was 72.9, 56.2, and 66.9%, respectively. The proportion of N that released from the three crop straws was 52.0, 54.4 and 54.9%, respectively. The zeta potentials and Brunauer, Emmett and Teller (BET) surface area of the rice, wheat and rape straw residues increased gradually as the decomposition period progressed. The water adsorption capacity of the rice straw was significantly affected during the decomposition period. The saturated water adsorption capacity of rice straw was the highest at 30 d of decomposition (4.17 g g–1) and then decreased slightly. The saturated water adsorption of wheat and rape straws reached the lowest value at 30 d and then gradually increased and became stable. All the results demonstrated that crop straw and straw residue can re-adsorb NH4+ ions from the surrounding solution. The re-adsorption was affected by the decomposition period and concentration of exogenous NH4+ and was independent of the crop species via the combined efforts of physical and chemical adsorption, ion exchange and water retention on residue surfaces. Future studies will focus on straw returning and N fertilizer application at different levels of moisture content of the soil reduce potential negative effects such as water-logging and excess N caused by the straw substrate.

Enhancing water adsorption capacity of acorn nutshell based activated carbon for adsorption thermal energy storage application

Adsorption thermal energy storage plays a vital role in supporting the availability of renewable energy. Activated carbons produced from local waste biomass have been attracting considerable attention in adsorption technology due to their unique properties and sustainability. However, their limitation in water vapor uptake hinders the practical application of this material. In this work, acorn nutshells were utilized as a base material to produce activated carbon. Air oxidation was performed as a versatile and low-cost technique to enhance the material’s properties and water adsorption capacity. By applying air oxidation as a post-treatment during material production, the amount of active functional groups and the water adsorption on activated carbon has been successfully enhanced. From the theoretical calculation, it is found that activated carbon–water working pairs shown promising performance to be used for adsorption thermal energy storage applications. The adsorption of water vapor on the post-treated-activated carbon releases the isosteric heat between 2400 kJ/kg to 2500 kJ/kg. Moreover, this study’s working pair can be driven by a temperature of less than 50 °C. From the results, it is confirmed that by controlling the adsorbent’s surface properties, activated carbon–water working pairs can be a promising way to provide alternative material and reduce the energy demand for driving the system.

Robust and conductive mesoporous reduced graphene oxide-silica hybrids achieved by printing and the sol gel route

Reduced graphene oxide (rGO) scaffoldings are used as templates to create lightweight 3D rGO/silica and rGO/silico-aluminate hybrids by a simple impregnation route and the sol-gel method. The printed rGO assemblies are infiltrated by the corresponding alkoxide precursor solution and gelled by exposure to ammonia vapours, producing an hybrid replica of the rGO structure. The hybrids show a significant prevalence of mesopores, with total porosity above 94 %, density of ∼ 0.1 g⋅cm−3 and high specific surface area (≥ 190 m2⋅g−1). As a result, the 3D composite materials show enhanced water adsorption capacity and hydrophilicity, display compressive strengths in the range 0.1 – 0.4 MPa, which scale with the proportion of silica (or Al-modified silica) on the hybrid scaffold, and electrical conductivities are above 60 S⋅m−1. These properties are very attractive for applications in the removal of pollutants, water filtering, catalysis, drug delivery, or energy production and storage.

Preparation and characterization of composite adsorbent LiCl/zeolite 13X for adsorption system

A novel composite adsorbent with high adsorption capacity, stable cycle performance and structure is developed. LiCl/zeolite 13X composite adsorbents with different LiCl content were synthesized by double solvents impregnation with alcohol and ethanol. The textural properties of composite adsorbents were characterized by nitrogen adsorption and scanning electron microscopy (SEM). The water adsorption performance of the composite adsorbents was tested, and the dynamic and equilibrium adsorption characteristics of the composite adsorbents were simulated by Polanyi potential theory and LDF model, respectively. Research on nitrogen adsorption suggested that because of the impregnated salt, composite adsorbents presented different pore structure pure. As the salt concentration of the LiCl solution increases, more salt is immersed into the pore channels of zeolite 13X, resulting in the LiCl content in the adsorbents increasing simultaneously. Water adsorption capacity of the composite adsorbent is not enhanced consistently with the increase in LiCl loading amount. After LiCl modification process, the water adsorption capacity increases little when the salt load is low, and then, the water adsorption capacity increases significantly with the increase in the salt load and finally decreases slightly. The sorption performance of CS30 with salt content of 16.7 wt% was optimal, and the maximum sorption capacity was 0.7 g/g, nearly 3.3 times than properties of zeolite 13X 0.21 g/g. As the number of cycles increases, the adsorption capacity of the composite adsorbent decreases slightly. The tenth cycle is only reduced by 8.67% compared to the first cycle.

Green adsorbents for copper (II) biosorption from waste aqueous solution based on hydrogel-beads of biomaterials

An innovative prototype machine was invented for hydrogel bead production, used for preparing novel hydrogel beads, based on biomaterials, fabricated from chitosan (CS), poly(vinyl alcohol) (PVA) and their blend for heavy metal removal from aqueous solution. The adsorption capacity of copper (II) ion onto the beads as adsorbents with their varying compositions and pH from aqueous solution was investigated. The properties of beads were determined using FTIR, SEM-EDX analysis and elemental mapping analysis, and water absorption measurement. The results showed that the CS, PVA and their blend were successfully crosslinked with glutaraldehyde solution. The swelling ratio, equilibrium water content and adsorption capacity depended on their compositions and pH. The spherical appearance of PVA hydrogel bead (PHB) exhibited the equilibrium swelling ratio higher than PVA/CS hydrogel bead (PCHB) and CS hydrogel bead (CHB), respectively. However, the adsorption capacity of copper (II) ion onto CHB was higher than PCHB and PHB, respectively. This behavior is due to their reactive sites being increased, resulting in the increase of interaction between copper (II) ion and CS molecules. Besides, the contact time directly affected the adsorption capacity in aqueous solution. Additionally, it was found that the pseudo-second-order exhibited the best fit for the kinetic studies, indicating the copper being limited by chemisorption process and the mechanism diffusion was controlled by intraparticle diffusion process. All the studied results indicated that hydrogel beads were an efficient and reusable adsorbent for the removal of copper (II) ion from aqueous solutions.

Higher Alcohols from Syngas with Graphite Oxide Modified CuFeMn Catalyst with Low CO2 Selectivity

The reasonable conversion of renewable resources such as biomass to fuels and chemical materials is vital important section for the natural carbon cycle and the effective solution for sustainable use of our planet’s resources. The process of syngas (from biomass gasification) to higher alcohols is an atomic efficiency reaction pathway and it attracts extensively attention with great potential applications and significance in science. The formation of CO2 during syngas conversion reaction in industrial scale is undesirable considering the less utilization value and greenhouse effect of CO2. In this work, we have prepared four catalysts with active components CuFeMn and support graphite oxide (GO) by traditional immersion preparation method. The introduction of GO improved the hydrophobic property of the catalyst. The H2O-TPD test confirmed that the GO modified catalyst performed a weaker water adsorption capacity than unmodified catalyst CuFeMn. Thus, the transfer rate of H2O on the modified catalyst surface increased and the residence time of H2O on the catalyst surface was greatly shortened. The undesired reaction of water-gas shift was suppressed and the CO2 formation was mainly limited in the catalyst surface during the syngas to higher alcohols reaction process. In addition, the effect of the amount of added GO was investigated and the catalyst CuFeMn-GO0.2-AR was found to exhibit the great performance for syngas to higher alcohols reactions.

Assessment of Soil and Fungal Degradability of Thermoplastic Starch Reinforced Natural Fiber Composite

High water absorption capacity and low biodegradation of fiber reinforced composites are the major drawbacks, which limit their applications in different sectors. Development of composites with complete biodegradability is challenging as biodegradability may be incomplete by lowering of its water adsorption capacity. In this work, a series of thermoplastic starch (TPS) reinforced jute (10–40 wt%) composites were developed by compression molding and measured by their mechanical properties. The composite with 30% jute showed the maximum tensile strength (27.3 MPa). Contact angle, and water absorption measurements exposed that composites are moderately hydrophobic in nature. Both soil burial and fungal degradation testing showed biodegradability of composites. Characterizations of optimized composite before and after biodegradation test, were carried out by FTIR, SEM and optical microscope. The present study showed promise on feasible applications of jute-starch composites in packaging, automobile sector, cutlery, indoor furnishing, etc. as a substitute of plastic-based composites.

Preparation of porous starch by α-amylase-catalyzed hydrolysis under a moderate electric field

Enzymatically-catalytic conversion of starch-based industrial waste into porous materials was enhanced by a moderate electric field (MEF). Changes in the hydrolysis rate, α-amylase activity and starch structure during MEF treatment (0–20 V, 0–400 Hz, room temperature and 0–2 h) were monitored and the hydrolyzed products were characterized by scanning electron microscopy, X-ray diffraction and water/oil adsorption analyses. The results showed that MEF enhanced enzymatic hydrolysis mainly by destroying starch structure, rather than by altering α-amylase activity. The average number of pores of hydrolyzed starch increased when voltage increased from 2 to 15 V, but a further increase of voltage caused the gelatinization of starch, thus making it unfavorable for the preparation of porous materials. The crystallinity of electrically-treated porous starches was decreased by 2.87–5.06%. The water and oil adsorption capacity of the porous starches was much higher than that of their native counterpart. Overall, this study extends the applications of electric field-based techniques in an enzymatic modification of biomaterials.

Environmentally friendly process based on a combination of ultrasound and peracetic acid treatment to obtain cellulose from orange bagasse

AbstractBACKGROUNDBrazil is responsible for 60% of the global production of orange juice, accounting for over three‐quarters of global orange juice exports, resulting in large quantities of orange bagasse (OB). This is an underutilized byproduct of the orange juice industry and corresponds to 50% of the fruit weight. The objectives of this study were to produce cellulose from OB using a combination of ultrasound and peracetic acid (PA) treatment, and to characterize the obtained materials according to their microstructure, crystallinity, thermal stability and water sorption behavior, and their cellulose, hemicellulose and lignin contents.RESULTSUltrasound pretreatment alone was not effective in altering the composition of OB. Samples subjected to both ultrasound and PA presented higher cellulose contents and lower hemicellulose and lignin contents in comparison to their respective samples undergoing PA treatment alone. The sample subjected to ultrasound for 10 min at a 30% amplitude combined with PA treatment for 24 h (USPA.24) resulted in the highest crystallinity index (54%), with 81.49% cellulose, 0.88% hemicellulose and 2.68% lignin. The increase in cellulose content of samples also resulted in lower water‐holding capacity, solubility and water adsorption capacity of samples.CONCLUSIONUltrasonication associated with PA treatment can be considered a promising approach and effective protocol for the extraction of cellulose from lignocellulosic residues, and it has the advantages of simplicity and environmental friendliness when compared to conventional methods, reducing the toxicity and amount of the resulting effluents. © 2020 Society of Chemical Industry (SCI)

Analysis on the mechanic resistance and water absorption capacity of prototype mortar with residual coconut mesocarp and fiber aggregates

Material physics has traditionally been used in the area of mechatronics and aeronautical engineering. However, in recent years, bioclimatic architecture has used physical principles and conservation of matter to evaluate the performance of buildings where the comfort and safety of its inhabitants are sought, with the mortar being an adequate alternative in minimizing heat transfer. However, this material is fragile and has a high risk of fragmentation. This problem has been addressed through the incorporation of inorganic aggregates to maximize their mechanical properties but the cost of production is high compared to the traditional process. This work proposes the analysis of cement-sand modules with coconut endocarp and mesocarp (coconut fiber) aggregates, by evaluating their mechanical resistance, under a compressing force, and permeability and comparing to current regulations. The results showed that coconut fiber has a large impact on the mechanical resistance of the prototypes: a proportion of fiber greater than 3% compromises the mechanical resistance of the prototypes due to the water adsorption capacity of coconut fiber. Whereas, the prototypes identified under the endocarp to fiber ratio of 10% to 1% showed the highest performance in the deformation tests under compression with respect to the modules without the presence of this waste material. The resulting mixture meets the Mexican standard for mortar and could be an alternative for avoiding the burning of plant residues in regions with an active coconut industry.

Water-bearing characteristics and their influences on the reservoir capacity in terrestrial shale reservoirs: A case study of the lower Jurassic Ziliujing Formation in the Northeast Sichuan Basin, China

The water content in shale reservoirs has a negative effect on reservoir space capacity. Compared with marine shale, terrestrial shale is characterized by higher clay content and lower total organic carbon (TOC), which is more sensitive to water and decreases gas storage capacity. However, it is still not fully understood how water is distributed in nanopores and how shale reservoir capacity is significantly weakened. In this study, a series of measurements were conducted methodically, including a moisture-equilibrated experiment, high-pressure mercury injection, gas adsorption, air-liquid contact angle, spontaneous imbibition and nuclear magnetic resonance, to investigate the water-bearing characteristics and effects of lacustrine shale. On the macroscopic scale, it was confirmed that clay shale displays the strongest water adsorption capacity and holds 2–3 times more water than siliceous shale. Clay minerals, especially montmorillonite, adsorb approximately 4 times more water than shale and 20 times more water than kerogen at a relative humidity (RH) of 98%. Meanwhile, clay shale with high TOC adsorbed less water. At the microscopic scale, the pore structure parameters of pore volume (PV) and specific surface area (SSA) can decrease up to 1/2 and 1/3, respectively, which based on our terrestrial shale samples at the RH of 98%. Furthermore, PV declines with increasing RH, primarily between 2.5 nm and 80 nm, while SSA also declines and fluctuates from 2.5 nm to 20 nm with increasing RH, which suggests that SSA is more susceptible to water than PV. When the RH increases from 0% to 98%, the minimum critical aperture (DCAmin) of the pore size shows an obvious shift from 2.5 nm to 7.5 nm, indicating that some nanopores are gradually damaged by water vapor and are unavailable for gas storage. In addition, water saturation in shale reservoirs maintains dynamic changes with thermal evolution. Finally, we proposed a multifactor controlled dynamic model and discussed the gas storage capacity of shale reservoirs with residual water. This study provides systematic and deep insight into water-bearing shale and is helpful for evaluating gas storage capacity in terrestrial reservoirs.

Kinetic analysis on water adsorption of thermally upgraded lignite

An in-situ water adsorption analyzer was designed and set up for obtaining water dynamic adsorption process of thermally upgraded lignite under relative humidity (RH) of 55%–85% at 20 °C and 30 °C. Four upgraded samples with different pore structures and oxygen functional groups were prepared at 120, 160, 240 and 320 °C. Grey correlation degree analysis method was used to study the correlation between water adsorption capacity and its influencing factors. The results showed that upgrading temperature was the dominant factor influencing water adsorption of upgraded coals compared to RH and environmental temperature. The dynamic adsorption process of water on coal could be well described by Intra-particle diffusion model, and it could be divided into surface adsorption stage, pore diffusion stage, and dynamic equilibrium stage. The rate-controlling factors of surface adsorption stage were oxygen functional groups and specific surface area, while those of pore diffusion stage were pore volume and pore size. During adsorption under RH 55%, water was firstly adsorbed on coal surface through oxygen functional groups with a relatively fast rate, which was orderly followed by formation of water clusters and capillary condensation of water in pores with a relatively slow rate.

Regulating the Electronic Structure and Water Adsorption Capability by Constructing Carbon‐Doped CuO Hollow Spheres for Efficient Photocatalytic Hydrogen Evolution

Copper(II) oxide featuring a narrow bandgap and low toxicity has been frequently applied in the visible-light-driven photocatalytic hydrogen evolution, but it suffers from large intrinsic overpotential and low water adsorption capacity. Herein, we report a self-templated strategy for the preparation of carbon-doped CuO hollow spheres (C-CuO HSs) through thermal transformation of a hierarchical MOF. The hierarchical Cu-MOFs not only act as a template to form interior voids during the thermal transformation, but also serve as precursors to dope C atoms into the CuO lattice. The as-synthesized C-CuO HSs exhibits remarkable photocatalytic performance with a H2 evolution rate of 67.3 mmol/g/h and the apparent quantum efficiency of 25.3 % at 520 nm in the present of eosin-Y photosensitizer. The high performance of C-CuO HSs is attributed to the hierarchical porous structure and modulated electronic structure of CuO by C-doping with well exposed reactive sites, high water adsorption capability, and low water reduction reaction barrier. The results presented in this work might shed light on the design of high-performance photocatalysts for various energy-related applications.