Intercalation-based inorganic materials that change their colours upon ion insertion/extraction lay an important foundation for existing electrochromic technology. However, using only such inorganic electrochromic materials, it is very difficult to achieve the utmost goal of full-colour tunability for future electrochromic technology mainly due to the absence of structural flexibility. Herein, we demonstrate an ultracompact asymmetric Fabry-Perot (F-P) nanocavity-type electrochromic device formed by using partially reflective metal tungsten as the current collector and reflector layer simultaneously; this approach enables fairly close matching of the reflections at both interfaces of the WO3 thin layer in device form, inducing a strong interference. Such an interference-enhanced device that is optically manipulated at the nanoscale displays various structural colours before coloration and, further, can change to other colours including blue, red, and yellow by changing the optical indexes (n, k) of the tungsten oxide layer through ion insertion.

Tw o-dimensional (2D) semiconductors have recently become attractive candidate substrates for surface-enhanced Raman spectroscopy, exhibiting good semiconductor-based SERS sensing for aw ider variety of application scenarios. However,the underlying mechanism remains unclear.Herein, we propose that surface defects playavital role in the magnification of the SERS performances of 2D semiconductors.Asaprototype material, ultrathin WO 3 nanosheets is used to demonstrate that surface defect sites and the resulting increased charge-carrier density can induce strong chargetransfer interactions at the substrate-molecule interface,t hereby improving the sensitivity of the SERS substrate by 100 times with high reproducibility.Further work with other metal oxides suggests the reduced dimension of 2D materials can be advantageous in promoting SERS sensing for multiple probe molecules.

Removal of nitrogen (N) and phosphorus (P) from water and wastewater through the use of various sorbents is often considered an economically viable way for supplementing conventional methods. Biochar has been widely studied for its potential adsorption capabilities for soluble N and P, but the performance of different types of biochars can vary widely. In this review, we summarized the adsorption capacities of biochars in removing N (NH4-N and NO3-N) and P (PO4-P) based on the reported data, and discussed the possible mechanisms and influencing factors. In general, the NH4-N adsorption capacity of unmodified biochars is relatively low, at levels of less than 20 mg/g. This adsorption is mainly via ion exchange and/or interactions with oxygencontaining functional groups on biochar surfaces. The affinity is even lower for NO3-N, because of electrostatic repulsion by negatively charged biochar surfaces. Precipitatio n of PO4-P by metals/metal oxides in biochar is the primary mechanism for PO4-P removal.Biochars modified by metals have significantly higher capacity to remove NH4-N, NO3-N, and PO4-P than unmodified biochar, due to the change in surface charge and the increase in metal oxides on the biochar surface. Ambient conditions in the aqueous phase, including temperature, pH, and co-existing ions, can significantly alter the adsorption of N and P by biochars, indicating the importance of optimal processing parameters for N and P removal. However, the release of endogenous N and P from biochar to water can impede its performance, and the presence of competing ions in water and wastewater poses practical challenges for the use of biochar for nutrient removal. In conclusion, more progress is needed to improve the performance of biochars and overcome challe nges before the widespread field application of biochar for N and P removal is realized.