Nitrogen and oxygen codoped porous carbons (NOCKs) were obtained by nitrogenization, preoxidation, and chemical activation. Considering the activation reagent amount and modification temperature, the pore structure conducive to CO 2 adsorption was obtained. NOCK-400-1 exhibits maximum CO 2 capacity of 6.77 mmol g −1 at 0 °C and 4.46 mmol g −1 at 25 °C, 1 bar. It also presents high dynamic CO 2 adsorption capacity under 15% CO 2 /85% N 2 at ambient temperature and excellent adsorption regenerability. The results show that the improvement of CO 2 adsorption performance is mainly due to the synergistic effect of codoping nitrogen and oxygen. The codoping method effectively improves the relative contents of pyrrolic-N, pyridinic-N, and phenolic hydroxyl with promoting the synthesis of amorphous carbon. Furthermore, the codoping method enhances the porosity of NOCKs with less consumption of KOH. The density functional theory (DFT) calculations also demonstrate two kinds of van der Waals actions (namely, dispersion interaction and electrostatic attraction) for CO 2 adsorption on the nitrogen and oxygen codoped carbon surface. Additionally, the physical adsorption mechanism on the heterogeneous surface of adsorbents is confirmed by adsorption isotherm and thermodynamic study. Therefore, nitrogen and oxygen codoped porous carbons are a promising sorbent for CO 2 capture, which provides the effective information for carbon design.

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The highly efficient removal of tetracycline (TC) from an aqueous solution was accomplished by using the raw shrimp shell waste (SSW) as an environmentally friendly adsorbent. The SSW without any treatment removed TC more efficiently than the SSW after being treated with HCl and NaOH solutions. The SSW was characterized using nitrogen adsorption–desorption isotherms, scanning electron microscopy alongside energy-dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, a thermogravimetric-derivative thermogravimetry analyzer, and a ζ-potential analyzer. The maximum adsorption capacity of 400 mg/L SSW was 229.98 mg/g for 36 h at 55 °C. Both the Langmuir isotherm model and the pseudo-second-order kinetic model well described the experimental data. According to the values of the Gibbs free energy and enthalpy changes, the TC adsorption by SSW proved to be spontaneous and endothermic. The TC adsorption process was controlled by intraparticle diffusion and liquid film diffusion.

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Chemical looping combustion (CLC) of coal is an attractive technology with inherent CO 2 separation and high energy utilization efficiency. The large-scale preparation of a cheap oxygen carrier with high attrition resistance challenges the scale-up step of CLC reactor systems. To improve the reactivity between the CaSO 4 /bentonite (CaBen) oxygen carrier and coal, CaSO 4 −Fe 2 O 3 /bentonite (CaFeBen) and CaSO 4 −K 2 CO 3 /bentonite (CaKBen), decorated by Fe 2 O 3 and K 2 CO 3 , respectively, were prepared in this work. The active component content, multi-cycle reactivity, and enhancement mechanism of two decorated oxygen carriers were investigated in a fluidized bed with steam as the gasification−fluidization medium. Finally, three types of coals, including lignite, bitumite, and anthracite, were used as fuel. The addition of Fe 2 O 3 and K 2 CO 3 can improve the reactivity of the CaBen oxygen carrier but degrade the attrition resistance slightly. The multiple-cycle experiments indicated that Fe 2 O 3 itself is the oxygen carrier for coal CLC with high reactivity, while K 2 CO 3 acts as the catalysis for coal gasification. The carbon conversion rate of the three coals that reacted with the CaKBen oxygen carrier was higher than that with CaFeBen as the oxygen carrier because of catalysis of potassium on the coal gasification reaction. However, the CaKBen oxygen carrier particles were seriously sintered, and the potassium content in the oxygen carrier reduced with the increasing redox cycles. The coals with high volatile and ash contents have a high instantaneous rate of carbon conversion reacted with two decorated oxygen carriers.

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Surface properties such as electronic structures and valence state determine the electrocatalytic activity in hydrogen evolution reactions (HERs). Herein, we prepared a novel orthorhombic CoSe 2 -NC (o-CoSe 2 -NC) electrocatalyst from hexagonal CoSe-NC (h-CoSe-NC) via a phase-transition method. As-prepared o-CoSe 2 -NC exhibited excellent HER activity with 147 mV at 10 mA cm −2 and a high stability (24 h). Density functional theory results revealed that the active sites for h-CoSe-NC in electrocatalytic hydrogen evolutions were the anion Se sites (ΔG H* = 0.34 eV). After the phase transition, Co sites (ΔG H* = 0.20 eV) in o-CoSe 2 -NC became more active than Se sites. Moreover, the dband central of Co in o-CoSe 2 -NC was closer to the Fermi level than that of h-CoSe-NC after the phase transition. Also, o-CoSe 2 -NC exhibited a metallic behavior with excellent electrical conductivity. This work not only prepared cost-effective cobalt selenide-based electrocatalysts but also highlighted the significance of the crystal phase in electrocatalytic hydrogen evolutions.