2D V₂C MXene/2D g-C₃N₄ nanosheet heterojunctions was exploited in this work, which almost completely removed dye pollutants (RhB and CV) with the removal ratio of 99.5%. This work is significant for the field of wastewater treatment.

Supercapacitors are considered as promising energy storage devices due to their high power density, fast charging/discharging process and long cycle life. The synthesis of Prussian blue analogues (PBAs) by the traditional co-precipitation method faces the problems of wastewater treatment, poor material reusability and low space utilization rate. Herein, an efficient and simple solid-state synthesis protocol is used to prepare diminutively granular and highly crystalline manganese hexacyanoferrate (MnHCF). MnHCF exhibits excellent electrochemical properties with the specific capacitance of 202.8 F g⁻¹ at a current density of 1 A g⁻¹ in a neutral electrolyte. At the same time, MnHCF has good cycle stability, which could maintain 95.63% after 8000 charge–discharge cycles. The maximum energy density of the two-electrode system with MnHCF as a positive electrode and YP-50F as a negative electrode is 18.89 W h kg⁻¹ at 981.25 W kg⁻¹ and a maximum power density of 7184.73 W kg⁻¹ at 7.52 W h kg⁻¹. The outstanding electrochemical properties can be attributed to smaller particle size and higher crystallinity to achieve faster ion diffusion and greater diffusion depth. Therefore, adopting a solid-state synthesis protocol is a promising approach to achieve low-cost and large-scale production of PBAs.

The excellent electrochemical performances of ternary hollow CuO/NiO/Co₃O₄ heterostructure could be the synergistic effect of the introduced heterojunction of CuO/NiO, hollow structure and various metal oxides.

Supercapacitors (SCs) have drawn much attention owing to their unique superiorities. The selection of electrode materials is significantly crucial as it influences SC performance. Defects such as low specific capacitance and poor rate performance need to be settled urgently to achieve enhanced SC performance. Here, we have developed an effective and facile strategy to prepare a binder-free nitrogen-doped graphene hydrogel (NDGH) as an electrode material. The electrochemical performance of NDGH was measured in three different electrolytes (2 M KOH, 1 M Na₂SO₄ and 1 M H₂SO₄), and it showed superior performance in 2 M KOH. NDGH had an outstanding specific capacitance of 224.1 F g⁻¹ at 1 A g⁻¹ and retained 80.7% of the capacitance at 10 A g⁻¹. Meanwhile, NDGH possessed good cycling stability, with 93% capacitance retention after 6000 cycles. The contributions of surface-controlled and diffusion-controlled processes to NDGH capacitance were analyzed in different electrolytes. Compared with 1 M Na₂SO₄ (52%) and 1 M H₂SO₄ (13%), superior surface-controlled contribution was observed in the 2 M KOH (73%) electrolyte at 10 mV s⁻¹. The symmetric supercapacitor (SSC) consisting of NDGH delivered an energy density of 14.3 W h kg⁻¹ at a power density of 582.8 W kg⁻¹ in the KOH electrolyte. These excellent electrochemical performance parameters could be achieved due to the synergistic effect of the multistage pore structure, nitrogen doping and binder-free hydrogel, which allow abundant electrochemical reactions to take place at the interface between the electrode materials and the electrolyte. This strategy may be further broadened to prominently enhance the specific capacitance and rate performance of graphene oxide.

This work provides a co-production and transformation technology of Cu ₂ (OH) ₂ CO ₃ , CuO to recover Cu resource from PCB etching waste solutions. The as-prepared high-purity nano-CuO (99.04 wt%) with impurity levels <0.12 wt% and Cl ⁻ <0.0015 wt%.