Hierarchical structure design of sea urchin Shell-Based evaporator for efficient omnidirectional Solar-Driven steam generation

Solar-driven steam generation (SSG) is regarded as a feasible solution to the problem of fresh water scarcity. Although several attempts have been devoted to increase the efficiency of solar-to-steam conversion, it remains difficult to fabricate cost-effective, steady, and multi-angle sunlight-absorbing evaporators from readily available biomass materials. Herein, a novel hierarchical structured SSG evaporator (PDA@Shell-NaClO) is developed through a simple, low-cost, and scalable etching treatment on discarded sea urchin (SU) shells. Attributing to the dedicatedly designed microneedles array structure and porous skeleton structure of the SU shell, this PDA@Shell-NaClO evaporator shows an outstanding average light absorption performance (>90%) in a broad range of angles from 0° to 60° and exceedingly high evaporation rate of 2.81 kg m^-2 h^-1 under one sun condition. Furthermore, the prepared evaporator also maintains an overall stable evaporation performance and exhibits an excellent durability for a long time of up to two weeks in actual seawater. This full-ocean biomass-based SSG evaporator with plentiful raw material availability offers innovative opportunities for large-scale fresh water production.

Investigation on the influence of additives on the oriented dissolution of calcite

Similar to the crystal growth process, additives have a strong influence on the dissolution process of crystals. Studies on the dissolution process may shed light on understanding the biomineralization and bioinspired crystallization process. The influence of different kinds of additives including surfactants and polymers on the dissolution process of calcite {104} planes was investigated in detail in this work. The additives can be classified into three kinds according to their influence on the dissolution process of calcite under different concentration windows. The additives show three different kinds of dissolution behaviors with the increase of additive concentrations according to the tomographic variation of the calcite surface after the dissolution process. There are four dissolution modes of calcite while changing the additive concentrations in the solution. Rhombohedral etch pits with [4[combining macron]41] and [481[combining macron]] step edges are formed on the calcite {104} planes after the dissolution process at low additive concentrations (mode I). Calcite micropyramids begin to appear on the calcite surface and the densities of micropyramids increase with the increase of the additive concentrations until they cover the entire calcite surface after the dissolution process at medium additive concentrations (mode II). Instead of micropyramids, large pyramids with [481[combining macron]] and [4[combining macron]41] step edges and a size of about 50 μm form after the dissolution process at high additive concentrations (modes III and IV). We propose that the different anisotropic dissolution behaviors of calcite are strongly related to the concentrations and the adsorption features of the additives on the calcite surface. The additives may act as inhibitors of calcite dissolution, possibly through adsorption on calcite surfaces without preferred adsorption, or adsorption at specific kink sites or step edges. The influence of additives on the oriented dissolution of calcite is generally related to the adsorption density and homogeneity of additives on the calcite substrates.

Investigation of the influence of cationic and anionic ions on the oriented dissolution of calcite

Cations (metal ions) have a more significant influence than anions on the oriented dissolution process of calcite and the metastable side faces and step edges of calcite micropyramids, probably due to the strong interaction between cations and CO₃²⁻.