The lack of freshwater resources, or the freshwater crisis, is an important issue in the resource field. One potential green and sustainable method to solve this problem is to implement solar energy-driven water evaporation to collect freshwater. Capitalizing on the low cost, high production yield, and simplified fabrication process properties of nonstoichiometric Co2.67S4 nanoparticles, we strategically designed and synthesized a Co2.67S4-deposited Teflon (PTFE) membrane for realizing efficient solar water evaporation and photothermal antibacterial properties under light irradiation. Compared with previously reported cellulose acetate and poly­(vinylidene fluoride) membranes, the PTFE membrane displayed significantly enhanced mechanical properties. Additionally, a Co2.67S4-deposited PTFE membrane with a hydrophobic treatment (termed as the Final-PTFE membrane) exhibited excellent durability. The light-to-heat conversion efficiency (η) of water evaporation reached a value of 82% for our as-prepared Final-PTFE membrane under two sun irradiation conditions. Moreover, the antibacterial mechanism observed by scanning electron microscopy was attributed to the thermal effect, which damaged the cell wall of bacteria. Our work highlights the great potentials of the Final-PTFE membrane as a versatile system for implementing solar energy-driven photothermal water evaporation and water purification.

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Solar-driven water evaporation provides a promising solution to the energy crisis and environmental issues. Capitalizing on the high photothermal conversion efficiency and excellent resistance to strong acids or strong alkalis of Pt3Ni–S nanowires, we strategically design and prepare a flexible Pt3Ni–S-deposited Teflon (PTFE) membrane for achieving efficient strong acid/alkaline water evaporation under simulated sunlight irradiation (1 sun). By comparing the surface morphology, mechanical properties, and water evaporation performance of the as-prepared three different membranes, we have screened out a high-performance photothermal membrane that has good hydrophobicity (water contact angle = 106°), strong mechanical properties, high light-to-heat conversion efficiency (η = 80%), and excellent durability (10 cycles in a range of pH = 1.2–12). In particular, we explore the mechanism of high surface mechanical properties of the as-prepared membrane using density functional theory. The results demonstrate that the related mechanism can be ascribed to two main reasons: (1) hydrogen bonds can be formed between the 2-pyrrolidone ring and PTFE-3 and (2) the O atom in PTFE-3 carries more negative charge (−0.19 |e|) than PTFE-1 (−0.16 |e|) and PTFE-2 (−0.15 |e|). Our work highlights the great potentials of a Pt3Ni–S-deposited PTFE membrane as a device for implementing solar energy-driven evaporation of industrial wastewater with strong acidity or alkalinity and provides a new strategy for improving the surface mechanical properties of a photothermal membrane.

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IntroductionThe COVID-19 vaccine donation process allegedly prioritised national interests over humanitarian needs. We thus examined how donors allocated vaccines by recipient country needs versus donor national interests and how such decisions varied across donation channels (bilateral vs COVAX with country earmarking) or exposure to foreign aid norms (membership status in the Development Assistance Committee—DAC).MethodsWe used the two-part regression model to examine how the probability of becoming a recipient country and the volume of vaccines received were associated with recipient countries’ needs (disease burden and GDP per capita), donor countries’ interests (bilateral trade volume and voting distance in the United Nations General Assembly) and recipient countries’ population size. The analysis further interacted the determinants with channel and DAC status.ResultsDonors preferentially selected countries with higher disease burden, lower GDP per capita, closer trade relations, more different voting preferences, and smaller populations. Compared with bilateral arrangements, COVAX encouraged more needs-based considerations (lower GDP per capita), less interest-based calculus (more distant economic relations and voting preferences) and larger population size. Compared with the DAC counterparts, the non-DAC donors focused more on politically and economically aligned countries but also on less economically developed countries. As for the volume of vaccines donated, countries received more vaccines if they had tighter trade relations with donors, more different voting patterns than donors, and larger populations. COVAX was associated with raising the volumes of vaccines to politically distant countries, and non-DAC donors donated more to countries with stronger trade relations and political alignment.ConclusionDonors consider both recipient needs and national interests when allocating COVID-19 vaccines. COVAX and DAC partially mitigated donors’ focus on domestic interests. Future global health aid can similarly draw on multilateral and normative arrangements.