Solid-liquid Interface Research Articles

Tailoring Second Coordination Sphere for Tunable Solid–Liquid Interfacial Charge Transfer toward Enhanced Photoelectrochemical H2 Production

AbstractThe recombination of photogenerated charge carriers severely limits the performance of photoelectrochemical (PEC) H2 production. Here, we demonstrate that this limitation can be overcome by optimizing the charge transfer dynamics at the solid–liquid interface via molecular catalyst design. Specifically, the surface of a p‐Si photocathode is modulated using molecular catalysts with different metal atoms and organic ligands to improve H2 production performance. Co(pda‐SO3H)2 is identified as an efficient and durable catalyst for H2 production through the rational design of metal centers and first/second coordination spheres. The modulation with Co(pda‐SO3H)2, which contains an electron‐withdrawing −SO3H group in the second coordination sphere, elevates the flat‐band potential of the polished p‐Si photocathode and nanoporous p‐Si photocathode by 81 mV and 124 mV, respectively, leading to the maximized energy band bending and the minimized interfacial carrier transport resistance. Consequently, both the two photocathodes achieve the Faradaic efficiency of more than 95 % for H2 production, which is well maintained during 18 h and 21 h reaction, respectively. This work highlights that the band‐edge engineering by molecular catalysts could be an important design consideration for semiconductor–catalyst hybrids toward PEC H2 production.

The electrochemistry of stable sulfur isotopes versus lithium

Sulfur in nature consists of two abundant stable isotopes, with two more neutrons in the heavy one (34S) than in the light one (32S). The two isotopes show similar physicochemical properties and are usually considered an integral system for chemical research in various fields. In this work, a model study based on a Li-S battery was performed to reveal the variation between the electrochemical properties of the two S isotopes. Provided with the same octatomic ring structure, the cyclo-34S8 molecules form stronger S-S bonds than cyclo-32S8 and are more prone to react with Li. The soluble Li polysulfides generated by the Li-34S conversion reaction show a stronger cation-solvent interaction yet a weaker cation-anion interaction than the 32S-based counterparts, which facilitates quick solvation of polysulfides yet hinders their migration from the cathode to the anode. Consequently, the Li-34S cell shows improved cathode reaction kinetics at the solid-liquid interface and inhibited shuttle of polysulfides through the electrolyte so that it demonstrates better cycling performance than the Li-32S cell. Based on the varied shuttle kinetics of the isotopic-S-based polysulfides, an electrochemical separation method for 34S/32S isotope is proposed, which enables a notably higher separation factor than the conventional separation methods via chemical exchange or distillation and brings opportunities to low-cost manufacture, utilization, and research of heavy chalcogen isotopes.

Constructing Sequential Type II Heterojunction CQDs/Bi2S3/TiNbO Photoanode with Superior Charge Transfer Capability Toward Stable Photoelectrochemical Water Splitting.

Efficient charge transfer and light-trapping units are pivotal prerequisites in the realm of Ti-based photoanode photoelectrochemical (PEC) water splitting. In this work, we successfully synthesized a ternary carbon quantum dots/Bi2S3 quantum dots/Nb-doped TiO2 nanotube arrays (CQDs/Bi2S3/TiNbO) composite photoanode for PEC water splitting. CQDs/Bi2S3/TiNbO composite photoanode exhibited a considerably elevated photocurrent density of 8.80 mA cm-2 at 1.23 V vs the reversible hydrogen electrode, which was 20.00 times better than that of TiO2 (0.44 mA cm-2). Furthermore, the CQDs/Bi2S3/TiNbO composite photoanode attested to exceptional stability, maintaining 92.54% of its initial current after 5 h of stability measurement. Nb-doping boosted the electrical conductivity, facilitating charge transfer at the solid-liquid interface. Moderate amounts of Bi2S3 quantum dots (QDs) and CQDs deposited on TiNbO provided abundant active sites for the electrolyte-photoanode interaction. Simultaneously, Bi2S3 QDs and CQDs synergistically functioned as light-trapping units to broaden the light absorption range from 396 to 530 nm, stimulating increased carrier generation within the composite photoanode. In comparison with pristine TiO, CQDs/Bi2S3/TiNbO photoanodes possessed a superior ability to promote interfacial reactions. This study may provide a strategy for developing high-performance Ti-based photoanodes with efficient charge transfer and light trapping units for highly driving solar-to-hydrogen conversion.

Tailoring Second Coordination Sphere for Tunable Solid-Liquid Interfacial Charge Transfer toward Enhanced Photoelectrochemical H2 Production.

The recombination of photogenerated charge carriers severely limits the performance of photoelectrochemical (PEC) H2 production. Here, we demonstrate that this limitation can be overcome by optimizing the charge transfer dynamics at the solid-liquid interface via molecular catalyst design. Specifically, the surface of a p-Si photocathode is modulated using molecular catalysts with different metal atoms and organic ligands to improve H2 production performance. Co(pda-SO3H)2 is identified as an efficient and durable catalyst for H2 production through the rational design of metal centers and first/second coordination spheres. The modulation with Co(pda-SO3H)2, which contains an electron-withdrawing -SO3H group in the second coordination sphere, elevates the flat-band potential of the polished p-Si photocathode and nanoporous p-Si photocathode by 81 mV and 124 mV, respectively, leading to the maximized energy band bending and the minimized interfacial carrier transport resistance. Consequently, both the two photocathodes achieve the Faradaic efficiency of more than 95 % for H2 production, which is well maintained during 18 h and 21 h reaction, respectively. This work highlights that the band-edge engineering by molecular catalysts could be an important design consideration for semiconductor-catalyst hybrids toward PEC H2 production.

Numerical study of heat transfer characteristics of phase change materials reinforced with porous media based on hybrid mesh

To address the drawbacks of inadequate energy density as well as utilization effectiveness in solar energy utilization, phase change energy storage offers a possible option. However, the low thermal conductivity of traditional phase change materials (PCMs) restricts the extent to which solar energy utilization can be enhanced. In this paper, the impact of the metal foam (MF) on the solid–liquid interface, the flow field, the enhancement heat transfer mechanism during the paraffin wax (PX) melting process and thermal storage characteristics was analyzed. Besides, a three-dimensional mathematical model of MF-PX using the hybrid mesh technique was established and software ANSYS-FLUENT was used for simulation. The results indicated that, the hybrid mesh exhibited a reduction of 52.75 % in mesh count compared to the unstructured mesh, resulting in 45 % reduction in computational time. Moreover, the hybrid mesh also showcased improved mesh quality that the unstructured mesh was mainly distributed in the range of 0.48–0.6, while within the range of 0.84–1.0 for the hybrid mesh. More important, the maximum relative error between experimental and simulation was 8.67 %, indicating that the model can make a reasonable prediction. With the proportions of MF increased from 0.11 % to 0.43 %, both the Rayleigh number (Ra) and its amplification decreased. At 800 s, the Ra decreased from 1.76E+07 to 1.20E+07, while the amplification of the Ra was reduced from 1.88E+07 to 1.30E+07. In addition, the natural convection proportions of CMF decreased from 96.31 % to 80.65 %. These observations indicated that natural convection was the primary heat transfer mechanism, and the conduction was enhanced by the increasing proportion of MF. Finally, in terms of heat storage characteristics, the heat storage capacity and heat storage rate of the composite PCM slightly decreased. The heat storage values decreased from 19.30 kJ to 18.66 kJ. Similarly, the heat storage rates decreased from 19.86 J/s to 18.81 J/s.

Numerical Simulation of the Influence of Non-Uniform ζ Potential on Interfacial Flow.

Zeta potential (ζ potential) is a significant parameter to characterize the electric property of the electric double layer (EDL), which is important at the solid-liquid interface. Non-uniform ζ potential could be developed on a chemically uniform solid-liquid interface due to external flow. However, its influence on the flow has never been concerned. In this investigation, we numerically studied the influence of non-uniform 2D ζ potential on the flow at the solid-liquid interface. It is found, that even without any external electric field and only considering the influence of 2D ζ potential distribution, swirling flow can be generated near EDL, according to the rotational electric volume force. The streamwise vortices, which are important in the turbulent boundary layer, are theoretically predicted in this laminar flow model when considering the 2D distribution of ζ potential, implying the necessity of considering the origin of streamwise vortices of the turbulent boundary layer from the perspective of electrokinetic flow. In addition, the ζ potential distribution can promote the wall shear stress. Therefore, more attention must be paid to shear-sensitivity circumstances, like biomedical, medical devices, and in vivo. We hope that the current investigation can help us to better understand the effect of charge distribution on interfacial flow and provide theoretical guidance for the development of related applications in the future.

Temperature-dependent water slip flow combined with capillary evaporation in graphene nanochannels

The discovery of ultrafast water flow in graphene channels holds significant implications for various applications like electronics cooling, thermally driven energy harvesting, and solar-driven desalination. However, existing slip flow measurements on graphene are confined to room temperature, limiting our understanding of temperature-dependent behaviors and constraining potential thermal applications. Here, we simultaneously measured water slip lengths and evaporation fluxes in graphene nanochannels with depths ranging from 78 to 290 nm, spanning a temperature range from room temperature up to 85 °C. This was achieved by employing a capillary flow model combined with evaporation, a factor that cannot be disregarded at elevated temperatures. The measured water slip lengths ranged from 20 nm to 80 nm, exhibiting a decrease with increasing temperature and an increase with greater channel depths. The temperature-dependent slip length can be attributed to enhanced momentum transfer at the solid-liquid interface at elevated temperatures, while the observed channel depth dependence may result from stronger electrical-double-layer interactions with decreased channel depths. Additionally, the capillary evaporation fluxes increased with rising temperatures and greater channel depths, effectively explained by the capillary evaporation theory.

A Study on the Adsorption of Rhodamine B onto Adsorbents Prepared from Low-Carbon Fossils: Kinetic, Isotherm, and Thermodynamic Analyses.

The aim of this study was to obtain a series of activated carbon samples by the chemical activation of low-rank coal. The precursor was impregnated with a NaOH solution. Activated carbons were characterized by determining their textural parameters and content of surface oxygen functional groups and by using an elemental analysis. The carbons were tested as potential adsorbents for the removal of liquid pollutants represented by rhodamine B. The effectiveness of rhodamine B removal from water solutions depended on the initial concentration of the dye, the mass of rhodamine B, and the pH and temperature of the reaction. The isotherm examination followed the Langmuir isotherm model. The maximum adsorption capacity of the rhodamine B was 119 mg/g. The kinetic investigation favored the pseudo-second-order model, indicating a chemisorption mechanism. The thermodynamic assessment indicated spontaneous and endothermic adsorption, with decreased randomness at the solid-liquid interface. The experiment revealed that a 0.1 M HCl solution was the most effective regenerative agent.

Freezing Shrinkage Dynamics and Surface Dendritic Growth of Floating Refractory Alloy Droplets in Outer Space.

The freezing shrinkage and dendritic growth are of great importance for various alloys solidified from high-temperature liquids to solids since they dominate microstructure patterns and follow-up processing. However, the microgravity freezing shrinkage dynamics is scarcely explored on the ground as it is hard to suppress the strong natural convection inside liquid alloys. Here, a series of in-orbit solidification experiments is conducted aboard the China Space Station with a long-term stable 10-5 g0 microgravity condition. The highest temperature up to 2265K together with substantial liquid undercoolings far from a thermodynamically stable state are attained for both Nb82.7Si17.3 and Zr64V36 refractory alloys. Furthermore, the solidification under microgravity of a droplet is simulated to reveal the liquid-solid interface migration, temperature gradient, and flow field. The microgravity solidification process leads to freezing shrinkage cavities and distinctive surface dendritic microstructure patterns. The combined effects of shrinkage dynamics and liquid surface flow in outer space result in the dendrites growing not only along the tangential direction but also along the normal direction to the droplet surface. These space experimental results contribute to a further understanding of the solidification behavior of liquid alloys under a weaker convection condition, which is often masked by gravity on the ground.

Prediction of adsorption of metal cations by clay minerals using machine learning

Adsorption of heavy metals by clay minerals occurs widely at the solid-liquid interface in natural environments, and in this paper, the phenomenon of adsorption of Cd2+, Cu2+, Pb2+, Zn2+, Ni2+ and Co2+ by montmorillonite, kaolinite and illite was simulated using machine learning. We firstly used six machine learning models including Random Forest(R), Extremely Forest(E), Gradient Boosting Decision Tree(G), Extreme Gradient Boosting(X), Light Gradient Boosting(LGB) and Category Boosting(CAT) to feature engineer the metal cations and the parameters of the minerals, and based on the feature engineering results, we determined the first order hydrolysis constant(log K), solubility product constant(SPC), and higher hydrolysis constant (HHC) as the descriptors of the metal cations, and site density(SD) and cation exchange capacity(CEC) as the descriptors of the clay minerals. After comparing the predictive effects of different data cleaning methods (pH50 method, Box method and pH50-Box method) and six model combinations, it was finally concluded that the best simulation results could be achieved by using the pH 50-Box method for data cleaning and Extreme Gradient Boosting for modelling (RMSE = 4.158 %, R2 = 0.977). Finally, model interpretation was carried out using Shapley explanation plot (SHAP) and partial dependence plot(PDP) to analyse the potential connection between each input variable and the output results. This study combines machine learning with geochemical analysis of the mechanism of heavy metal adsorption by clay minerals, which provides a different research perspective from the traditional surface complexation model.

Modeling coupled growth and motion of solid-air dendrite induced by convection in liquid hydrogen using phase-field lattice Boltzmann method

The safety hazard arising from the growth, condensation and accumulation of trace air in liquid hydrogen deserves attention. In order to predict the microstructural growth evolution and oxygen solute segregation distribution characteristics during solid-air dendrite motion induced by solution convection, a partially saturated bounce-back lattice Boltzmann coupled non-isothermal phase field method (PSLBM-PF) is proposed in this study. The partially saturated bounce-back lattice Boltzmann method (PSLBM) is employed to calculate the flow field and the forces and moments between the fluid and solid phases, and the phase field method (PF) is utilized for the computation of the growth of solid-air dendrites and the distribution of solute segregation. The motion of solid-air dendrites is determined by the momentum equation. The accuracy of the calculated interaction forces between fluid and solid phases was validated through the sedimentation process of circular particles in the liquid, and the capability of the present model to preserve the shape during solid-air dendrite motion (translational and rotational) was confirmed. Subsequently, this model was employed to investigate the growth and sedimentation motion of solid-air dendrites with different growth orientations in the solution. During dendrite settlement, the growth of the lower dendrite arms is promoted, while the settlement velocity and the solid phase fraction are almost unaffected by the growth orientation. Then, the differences in morphology evolution and solute distribution under conditions of forced convection for both stationary and motion are comparatively investigated, utilizing the free growth of solid-air dendrites under convection-free conditions as a reference. Finally, the model was utilized to study the growth of individual solid-air dendrites as well as translational and rotational motion under the action of shear flow. The presence of convection significantly alters the solute and temperature distributions at the solid-liquid interface, thereby influencing the dendrite growth process. The simulation results indicate that this model can predict the solid-air dendrites microstructural growth evolution and oxygen solute segregation distribution accompanying the convection and motion.

Reaction Thermodynamics of Zerovalent Iron and Hexavalent Chromium at the Solid-Liquid Interface and in Solution.

Zerovalent iron (Fe0) is a promising candidate for remediating hexavalent chromium (Cr(VI)) via adsorption and (or) reduction. Herein, the reaction between Fe0 and Cr(VI) at the solid-liquid interface and in solution under varying pHs was inspected using the methodology of equilibrium thermodynamics. First, species distribution functions of aqueous Cr(VI), Cr(III), Fe(III), and Fe(II) are deduced to illuminate the quantitative distribution of aqueous metal species. Second, the plausible reaction at pH = 0-14 either at the solid-liquid interface or in solution is determined according to the species distribution function. Third, the spontaneity of each reaction is evaluated via a thermodynamic calculation based on the van't Hoff equation. The results present the following. (1) At the solid-liquid interface, the redox reaction 2Cr(VI) + 3Fe0 → 2Cr(III) + 3Fe(II) is spontaneous, inducing complete Cr(VI) → Cr(III) reduction at pH = 0-14. Especially, the high spontaneity of the redox reaction is mainly ascribed to Fe0 oxidation, which serves as a highly spontaneous subreaction. (2) In solution, the redox reaction Cr(VI) + 3Fe(II) → Cr(III) + 3Fe(III) is nonspontaneous at pH = 6 and 7, whereas it is spontaneous at pH = 6-7, 0-5, and 8-14. Accordingly, no Cr(VI) → Cr(III) reduction at pH = 6-7 and complete Cr(VI) → Cr(III) reduction at pH = 0-5 and 8-14 are expected. Particularly, the nonspontaneity of the Cr(VI) reduction at pH = 6-7 is majorly attributed to water ionization, which is involved as a highly nonspontaneous subreaction. On the contrary, the spontaneity of the Cr(VI) reduction at pH = 0-5 and 8-14 is mainly owing to acid-base neutralization, which is involved as a highly spontaneous subreaction. This work may deepen our knowledge about the chemistry involved in hexavalent chromium remediation by the zerovalent iron.

Exploring anomalous nanofluidic transport at the interfaces

AbstractTransport of ions and water is essential for diverse physiological activities and industrial applications. As the dimension approaches nano and even angstrom scale, ions and water exhibit anomalous behaviors that differ significantly from the bulk. One of the key reasons for these distinctive behaviors is the prominent influence of surface effects and related transport properties occurring at the interface under such (sub)nanoconfinement. Therefore, exploring nanofluidic transport at the interfaces could not only contribute to unraveling the intriguing ion and water transport behaviors but also facilitate the development of nanofluidic devices with tunable mass transport for practical applications. In this review, we focus on three crucial interfaces governing ion and water transport, namely liquid–gas interface, liquid–solid interface, and liquid–liquid interface, with emphasis on elucidating their intricate interfacial structures and critical roles for nanofluidic transport phenomena. Additionally, potential applications associated with liquid–gas, liquid–solid, and liquid–liquid interfaces are also discussed. Finally, we present a perspective on the pivotal roles of interfaces on nanofluidics, as well as challenges in this advancing field.

Nanostructured lubricant additives for titanium alloy: Lubrication by the solid-liquid interface with Coulomb repulsion

AbstractIn this work, the advantage of Coulomb repulsion in the intermolecular forces experienced by molecules on the solid-liquid nanosized contact interface is taken, and the superior friction-reducing property of Cu3(PO4)2·3H2O (CuP) oil-based additives has been confirmed for titanium alloy. Three-dimensional (3D) CuP nanoflowers (CuP-Fs) with a strong capillary absorption effect are prepared to achieve the homogeneous mixing of solid CuP and lubricating oil. Lubrication by CuP-Fs additives for titanium alloy, friction coefficient (COF) can be reduced by 73.68%, and wear rate (WR) reduced by 99.69%. It is demonstrated that the extraordinary friction-reducing property is due to the repulsive solid-liquid interface with low viscous shear force originating from Coulomb repulsion between polar water molecules in CuP and non-polar oil molecules. However, any steric hindrance or connection between this repulsive solid-liquid interface will trigger the adhesion and increase the viscous shear force, for example, dispersant, hydrogen bondings, and shaky adsorbed water molecules. Besides, the lamellar thickness of CuP and the molecular size of lubricant both have a great influence on tribological properties. Here the lubrication mechanism based on interface Coulomb repulsion is proposed that may help broaden the scope of the exploration in low-friction nanomaterial design and new lubricant systems.

CO2 sequestration by ammonia-enhanced phosphogypsum mineral carbonation: Development and optimization of reaction kinetic model

Comparing of existing kinetic models for direct mineral carbonation by solid waste, an optimized kinetic model was developed to depict the relationship between phosphogypsum carbonation ratio and reaction time. Based on the optimized model, the reaction mechanism of CO2 sequestration by ammonia-enhanced phosphogypsum mineral carbonation was analyzed. The experimental results show that, under specific conditions, including an ammonia ratio of 2.3, room temperature (25 °C), a liquid–solid ratio of 5:1, a gas flow rate of 200 mL/min, and a rotational speed of 500 rpm, phosphogypsum achieved its peak carbonation efficiency of 91 % within 30 min. The optimized model fitting curve has a high consistency with the experimental data, and the average R2 value is 0.991. The process of ammonia-enhanced phosphogypsum mineral carbonation comprises three distinct sub-processes. It is consisted of mass transfer in gas–liquid interface and solid–liquid interface, respectively, and product layer diffusion. Among them, the gas–liquid mass transfer is identified as the rate-controlling step in the mineral carbonation process. The present study provides a basis for the operation optimization and large-scale utilization of phosphogypsum mineral carbonation.

Soft Millirobot Capable of Switching Motion Modes on the Fly for Targeted Drug Delivery in the Oviduct.

Small-scale magnetic robots with fixed magnetizations have limited locomotion modes, restricting their applications in complex environments in vivo. Here we present a morphology-reconfigurable millirobot that can switch the locomotion modes locally by reprogramming its magnetizations during navigation, in response to distinct magnetic field patterns. By continuously switching its locomotion modes between the high-velocity rigid motion and high-adaptability soft actuation, the millirobot efficiently navigates in small lumens with intricate internal structures and complex surface topographies. As demonstrations, the millirobot performs multimodal locomotion including woodlouse-like rolling and flipping, sperm-like rotating, and snake-like gliding to negotiate different terrains, including the unrestricted channel and high platform, narrow channel, and solid-liquid interface, respectively. Finally, we demonstrate the drug delivery capability of the millirobot through the oviduct-mimicking phantom and ex vivo oviduct. The magnetization reprogramming strategy during navigation represents a promising approach for developing self-adaptive robots for performing complex tasks in vivo.

Static-dynamic wetting characteristics and microscopic synergistic mechanism of compound surfactant on coal dust with different metamorphic degrees

The compound surfactant has a synergistic effect on the wetting ability of coal dust. In the study, the wettability of compound surfactant on coal dust with different metamorphic degrees was studied from static wetting experiment, dynamic wetting experiment, and micro molecular simulation. The results showed that the contact angle of the anionic-nonionic compound surfactant solution on any coal sheet was significantly smaller than that of the single component, which was 14.04%～63.31% lower than that of the single component. The contact angle of the anionic-anionic compound surfactant on the six kinds of coal dust test pieces was not smaller than the contact angle of each single component, only a compromise of contact angle of single component. The dust suppression efficiency of the gas coal in 0.025 wt% fatty acid methyl esters ethoxylate sulfonate (FMES) and 0.025 wt% coconutt diethanolamide (CDEA) compound solution was the highest, which was 78.4%. Lignite coal, long flame coal, non-caking coal, coking coal, and anthracite all have the highest dust suppression efficiency when sprayed with 0.025 wt% sodium alcohol ether sulphate (AES) and 0.025 wt% CDEA, which were 91.53%, 88.24%, 85.7%, 73.25%, and 80.57%, respectively. For any metamorphic degree of coal sample dust, the anionic-nonionic compound surfactant shows obvious synergistic effect on improving the wettability of coal dust. Furthermore, when the surfactant is adsorbed on the surface of coal molecules, the concentration of water molecules on the surface of coal molecules is increased, the hydrophilicity of the solid–liquid interface is improved, and the water molecules are more intensely diffused on the surface of coal dust. And the absolute value of the adsorption energy of the surfactant on the surface of the coal dust is higher, and the more hydrogen bonds formed by the hydrophilic groups, the better the wettability of the coal dust surface.

A Dual-Mode Triboelectric Nanogenerator for Efficiently Harvesting Droplet Energy.

Triboelectric nanogenerator (TENG) is a promising solution to harvest the low-frequency, low-actuation-force, and high-entropy droplet energy. Conventional attempts mainly focus on maximizing electrostatic energy harvest on the liquid-solid surface, but enormous kinetic energy of droplet hitting the substrate is directly dissipated, limiting the output performance. Here, a dual-mode TENG (DM-TENG) is proposed to efficiently harvest both electrostatic energy at liquid-solid surface from a droplet TENG (D-TENG) and elastic potential energy of the vibrated cantilever from a contact-separation TENG (CS-TENG). Triggered by small droplets, the flexible cantilever beam, rather than conventional stiff ones, can easily vibrate multiple times with large amplitude, enabling frequency multiplication of CS-TENG and producing amplified output charges. Combining with the top electrode design to sufficiently utilize charges at liquid-solid interface, a record-high output charge of 158 nC is realized by single droplet. The energy conversion efficiency of DM-TENG is 2.66-fold of D-TENG. An array system with the specially designed power management circuit is also demonstrated for building self-powered system, offering promising applications for efficiently harvesting raindrop energy.

Effect of the irradiation intensity on the photo-thermal conversion performance of composite phase change materials: An experimental approach

Composite phase change materials (CPCM) containing photo absorbers are regarded as promising conversion and thermal energy storage materials for solar energy. Understanding the impact of irradiation intensity on the photo-thermal conversion process is of crucial significance for improving the photo-thermal conversion efficiency (PTCE) of CPCM. However, previous studies have overlooked the evolution of temperature patterns and the solid-liquid phase interface in CPCM, posing challenges in revealing photo-thermal conversion characteristics. In response to these challenges, the present study introduces an improved test method that integrates monitoring plane and infrared thermography. Paraffin/graphite nanoparticles CPCM are used as conversion and thermal storage material. The results show that the dominated heat transfer mode in different stages is different, and the natural convection within the liquid CPCM has enhanced the melting process. When the irradiation intensity is increased from 450 W/m2 to 1250 W/m2, the average temperature and average charging rate increase by 33.75% and 197.27%, respectively. At an irradiation intensity of 1050 W/m2, the CPCM achieves the highest overall PTCE of 42.40%, which is an 8.85% increase in contrast to the irradiation intensity of 450 W/m2. The results provide guidance for improving the PTCE of CPCM in the application of direct absorption solar collectors.

Evaporation-driven interfacial restructuring induces highly efficient methanogenesis of waste biomass

Methanogenesis of waste biomass (WB) is a promising method for global sustainable development, reduction of pollution and carbon emission levels, and recovering bioenergy. Unlike in the methanogenesis of organic wastewater, in which microbial cells come into direct contact with the dissolved substrate, the ‘solid–liquid–solid’ modes in WB and between WB and microbial cells, which involve numerous solid–liquid interfaces, greatly hinder the methanogenesis efficiency of WB. Amongst all WB, waste activated sludge is the most complex, poorly biodegradable and representative. Herein, we highlight the role of water evaporation-driven solid-liquid interfacial restructuring of sludge in determining its methanogenesis efficiency. Non-free water evaporation increased surface roughness and adhesion, and compressed pore structure with numerous capillaries in sludge, resulting in a new solid-liquid interface of sludge with great capillary force and highly ordered interfacial water molecules, which provides an extremely favourable condition for high mass transfer and proton-coupled electron transfer (PCET) in sludge. This restructuring was confirmed to induce the enhancement of solid–liquid interfacial noncovalent interactions and electron transfer efficiency in the subsequent methanogenesis process (P < 0.05), promoting the effective contact between the sludge substrate and microbial cells, thereby enriching the methanogenic consortia (i.e., Clostridia and Methanosarcina were increased by 290.0 % and 239.7 %, respectively) and improving the activities of key enzymes. Stable isotope tracing and metagenomic analysis further reveal that this restructuring promoted the participation of water molecules in the methane formation by PCET-driven release of protons from water, and enhanced main methanogenesis metabolic pathways, especially the metabolic pathway of CO2-reduction methanogenesis (+65.2 %), thereby resulting in a great advance in methane generation (+147 %, P < 0.001). The findings can provide a reference for regulating directional anaerobic biotransformation of water-rich multiphase complex substrates by interfacial restructuring inducement.