Mechanisms of salt rejection at the ice-liquid interface during the freezing of pore fluids in the seasonal frozen soil area

Seasonal frozen soil accounts for about 53.50%of the land area in China.Frozen soil is a complex multiphase system where ice,water,soil,and air coexist.The distribution and migration of salts in frozen soil during soil freezing are notably different from those in unfrozen soil areas.However,little knowledge is available about the process and mechanisms of salt migration in frozen soil.This study explores the mechanisms of salt migration at the ice-liquid interface during the freezing of pore fluids through batch experiments.The results are as follows.The solute concentrations of liquid and solid phases at the ice-liquid interface(C*_(L),C*_(S))gradually increased at the initial stage of freezing and remained approximately constant at the middle stage.As the ice-liquid interface advanced toward the system boundary,the diffusion of the liquid phase was blocked but the ice phase continued rejecting salts.As a result,C*_(L)and C*_(S)rapidly increased at the final stage of freezing.The distribution characteristics of solutes in ice and the liquid phases before C*_(L)and C*_(S)became steady were mainly affected by the freezing temperature,initial concentrations,and particle-size distribution of media(quartz sand and kaolin).In detail,the lower the freezing temperature and the better the particle-size distribution of media,the higher the solute proportion in the ice phase at the initial stage of freezing.Meanwhile,the increase in concentration first promoted but then inhibited the increase of solutes in the ice phase.These results have insights and scientific significance for the tackling of climate change,the environmental protection of groundwater and soil,and infrastructure protection such as roads,among other things.

Tree‑Inspired Structurally Graded Aerogel with Synergistic Water,Salt,and Thermal Transport for High‑Salinity Solar‑Powered Evaporation

Solar-powered interfacial evaporation is an energy-efficient solution for water scarcity.It requires solar absorbers to facilitate upward water transport and limit the heat to the surface for efficient evaporation.Furthermore,downward salt ion transport is also desired to prevent salt accumulation.However,achieving simultaneously fast water uptake,downward salt transport,and heat localization is challenging due to highly coupled water,mass,and thermal transport.Here,we develop a structurally graded aerogel inspired by tree transport systems to collectively optimize water,salt,and thermal transport.The arched aerogel features root-like,fan-shaped microchannels for rapid water uptake and downward salt diffusion,and horizontally aligned pores near the surface for heat localization through maximizing solar absorption and minimizing conductive heat loss.These structural characteristics gave rise to consistent evaporation rates of 2.09 kg m^(-2) h^(-1) under one-sun illumination in a 3.5 wt%NaCl solution for 7 days without degradation.Even in a high-salinity solution of 20 wt%NaCl,the evaporation rates maintained stable at 1.94 kg m^(-2) h^(-1) for 8 h without salt crystal formation.This work offers a novel microstructural design to address the complex interplay of water,salt,and thermal transport.

Continuous water-water hydrogen bonding network across the rim of carbon nanotubes facilitating water transport for desalination

The development of membranes featuring carbon nanotubes(CNTs)have provided possibilities of next-generation solar desalination technologies.For solar desalination,the microstructures and interactions between the filter membrane and seawater play a crucial role in desalination performance.Understanding the mechanisms of water evaporation and ion rejection in confined pores or channels is necessary to optimize the desalting process.Here,using non-equilibrium molecular dynamics simulations,we found that continuous water-water hydrogen bonding network across the rims of CNTs is the key factor in facilitating water transport through CNTs.With the continuous hydrogen bonding network,the water flux is two times of that without the continuous hydrogen bonding network.In CNT arrays,each CNT transports water molecules and rejects salt ions independently.Based on these observations,using CNT arrays consisted with densely packed thin CNTs is the most advisable strategy for evaporation desalination,possessing high transport flux as well as maintaining high salt rejection.

Hydrophobic polyethersulfone porous membranes for membrane distillation

Membrane distillation （MD） is a thermal, vapor-driven transportation process through micro porous hydrophobic membranes that is increasingly being applied to seawater and brine desalination processes. Two types of hydrophobic microporous polyethersulfone fiat sheet membranes, namely, annealed polyethersulfone and a polyethersulfone/tetraethoxysilane （PES/TEOS） blend were prepared by a phase inversion process. The membranes were characterized and their performances were investigated using the vacuum membrane distillation of an aqueous NaCI solution. The performances of the prepared membranes were also compared with two commercially available hydrophobic membranes, polyte- trafluorethylene and polyvinylidene fluoride. The influence of operational parameters such as feed temperature （25-65 ℃）, permeate vacuum pressure （200 800 mbar）, feed flow rate （8-22 mL/s） and feed salt concentration （3000 to 35000 mg/L） on the MD permeation flux were investigated for the four membranes. The hydrophobic PES/TEOS membrane had the highest salt rejection （99.7%） and permeate flux （86 kg/（m^2 -h）） at 65 ℃, with a feed of 7000 ppm and a pressure of 200 mbar.

Stretchable and Superhydrophilic Polyaniline/Halloysite Decorated Nanofiber Composite Evaporator for High Efficiency Seawater Desalination

Here,authors report on composition of a stretchable,mechanically durable and superhydrophilic polyaniline(PANI)/hal-loysite nanotubes(HNTs)decorated PU nanofiber(PANI/HNTs@PU).The polymer nanofibers are placed as the core and PANI/HNTs makes the shell section.The PANI/HNTs creates a membrane with outstanding light absorption and photo-thermal conversion performance.The strong solar absorption capability and superhydrophilicity of the PANI/HNTs@PU remain almost unchanged during stretching,abrasion,and ultrasonic washing tests,exhibiting superior surface stability and durability.When the PANI/HNTs@PU is used for the interfacial evaporation,the evaporation rate and efficiency reach as high as 1.61 kg m^(-2) h^(-1) and 94.7%,respectively.No salt precipitation is observed on the solar absorber surface even under a high salinity or during the long term or cyclic evaporation test.Furthermore,the excellent interfacial evaporation function is maintained when the nanofiber composite is mechanically stretched.The PANI/HNTs@PU based evaporation device shows promising applications in high performance solar desalination.