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With the rapid development of electronics, the application and research of two-dimensional materials have been at the forefront of the world’s scientific research. Black phosphorus (BP) has the advantages of large specific surface area, anisotropy, band tunability, high electrical conductivity and high theoretical specific capacity, which make it very promising for research in the fields of medicine, aerospace and electrochemistry. This paper calculates the electronic structure and adsorption properties of BP in water for different heavy metal ions of Pb${}^{2+}$, Hg${}^{2+}$ and Cd${}^{2+}$, including adsorption energy, bandgap, electron density and Mulliken population analysis, based on the first-principles approach of density generalized theory. First principles are quantum mechanical calculations based on density functional theory (DFT), which is a dominant well-developed method in the field of materials simulations, with low errors and high efficiency, especially in systems containing metallic particles. The results showed that the Pb${}^{2+}$ adsorption system in water was more stable than the Hg${}^{2+}$ adsorption system and the Cd${}^{2+}$ adsorption system. The bandgap values of 0.617, 0.785 and 0.715eV of BP after adsorption of Pb${}^{2+}$, Hg${}^{2+}$ and Cd${}^{2+}$ in water are smaller compared to 0.891eV of intrinsic BP, and its properties change from direct bandgap semiconductor to indirect bandgap semiconductor. The higher the stability of a system for the adsorption of different heavy metal ions by BP, the higher the internal electron activity of the adsorption system and the amount of electron transfer. Meanwhile, it is concluded that the electrons mainly transfer from P to heavy metal ions in all the adsorption systems.

The electron transfer of the BP-Pb${}^{2+}$, Hg${}^{2+}$, and Cd${}^{2+}$ adsorption system occurs mainly in the p, s, and s/p orbitals, respectively. The above content investigated the electronic structure changes and internal electron transfer of heavy metal ions adsorbed by black phosphorus in water, expecting to provide a new reference basis for the detection of heavy metal ions in industrial wastewater using black phosphorus.

The density functional theory has been used to study the adsorption performance of polluting Cu${}^{2+}$ and Zn${}^{2+}$ ions on defective graphene. Compared to intrinsic graphene, the adsorption distance between defective graphene and Cu${}^{2+}$/Zn${}^{2+}$ decreases greatly, and the adsorption energy and charge transfer amount increases significantly. The calculation of charge density demonstrates that clear hybridization happens between defective graphene and Cu${}^{2+}$/Zn${}^{2+}$ ions, suggesting the formation of chemical adsorption. The frontier orbit analysis shows that defective graphene has greater electrical sensitivity after adsorbing Cu${}^{2+}$/Zn${}^{2+}$ ions. Therefore, defective graphene could be a potential material for the treatment of contaminating heavy metal ions.

Novel 4,4′-{(diphenylmethylene)bis(4,1-phenylene)bis(oxy)} bridged ball-type metal-free, zinc(II), cobalt(II) and iron(II) ball-type metallophthalocyanines were achieved by the reaction of the bisphthalonitrile derivative in 2-dimetylaminoethanol. The isolation of the metal-free and metallophthalocyanines were carried out by both planar and column chromatography and also by hot soxhalet extraction. Their structures have been characterized by infrared, ultraviolet-visible, ¹H nuclear magnetic resonance and matrix assisted laser desorption/ionization mass spectroscopies. The redox characters of the ball-type metallophthalocyanines have been investigated by cyclic voltammetry, square wave voltammetry, controlled potential coulometry and spectroelectrochemistry in nonaqueous media. The investigation suggested that the ball-type complexes form ring-based and/or metal-based mixed-valence species as a result of the remarkable interaction between the two Pc rings and/or metal centers. Furthermore, these species were found to be stable as evidenced by the splitting of the relevant redox processes. The electrocatalytic oxygen reducing performances of the dinuclear ball-type complexes were also studied. The compound involving Fe(II) centers at the phthalocyanine cores displayed higher catalytic performance towards oxygen reduction than those of other ones. By using these compounds as sensing materials, a flow type quartz crystal microbalance sensor was developed for the detection of small concentrations of heavy metal ions. A cadmium ion sensitivity of 2.85 × 10⁴ Hz/mg.L${}^{-1}$ was observed with ball-type iron(II) phthalocyanine coated quartz crystal microbalance sensor. Detection of other metal ions including Fe${}^{2+}$, Zn${}^{2+}$, Ag${}^{2+}$ and Sn${}^{2+}$ were also performed. The results indicated that 1– 4 functionalized quartz crystal microbalance sensors can be used for the detection of heavy metal ions in aqueous solution. Partition coefficients obtained from the linear response regimes of the calibration curves are in the 8.6 × 10⁴–5.4 × 10⁵ range. Results show that the minor structural difference between metal free and metallophthalocyanine poses significant impact on metal ion partitioning.

Magnetic and fluorescent-based sensors have demonstrated widely applications due to their easily recycle and quickly optical response. However, the complex synthesis and weaker function of these sensors limit their practical applications. Herein, an unmodified, magnetic-functionalized carbon dots-based fluorescent sensor has been developed for label-free detection of pH and Cu${}^{2+}$ with high sensitivity. The sensors can not only reversibly quench and recover the fluorescence signals in response to the variation of surrounding environment including pH and Cu${}^{2+}$, but also be used as a high-efficiency recyclable adsorbent for removing Cu${}^{2+}$, Hg${}^{2+}$, Cr${}^{3+}$ and Pb${}^{2+}$ from aqueous solution.

The development of wastewater treatment agents with high treatment capacity and efficient separation is crucial for the remediation of heavy metal ions and organic dye wastewater. In this study, a polyrhodanine functional magnetic-activated carbon composite (PR-mAC) was synthesized via a one-step co-precipitation method combined with chemical oxidation polymerization. As an innovative water treatment agent, PR-mAC possesses not only environmentally friendly and easily obtainable raw materials but also magnetic properties that facilitate its reusability. Notably, PR-mAC exhibited remarkable removal efficiency towards lead ion (Pb(II)) and malachite green (MG). Experimental results demonstrated that the adsorption of Pb(II) and MG followed quasi-second-order kinetic model, while the Hill isothermal adsorption model and Redlich–Peterson isothermal adsorption model were suitable for Pb(II) and MG removal, respectively. All adsorption processes were spontaneous endothermic reactions. The maximum adsorption capacities reached 223.71 mg/g and 315.46mg/g, respectively. Even after undergoing 5 cycles, the material maintained satisfactory removal performance for Pb(II) and MG pollutants. Therefore, the prepared PR-mAC represents an optimal agent for wastewater treatment due to its effective capability in removing both metal ions and dyes.