Na Oa-assited Fabrication Of Ring-like Layered Double Hydroxides And Its Photo-/Electro-chemistry Performance

Hydrotalcite also identified as layered double hydroxides（LDHs）consisting of divalent and trivalent metal cations in the host layers and charge-balancing anions in the interlayer galleries.The wide tunability of the types or molar ratios(M²⁺/M³⁺)of metal cations,the nature of interlayer anions,and the structures of crystals afforded a large variety of functionality and hybrid possibility for applying LDHs with a uniform distribution of active sites as adsorbents,catalysts,photocatalysts,energy conversion and storage devices,and drug delivery hosts.Traditional methods to directly synthesize LDHs,such as co-precipitation method,solvothermal method,and calcine-recovering method,are well-developed by far.However,LDHs prepared by such methods often tend to adopt a hexagonal plate-like morphology,which determined by its hexagonal crystal structure and an inherent 2D growth feature.The controllable composition and structure of nanomaterials may greatly enhance its performance.Hence,it is challenging and vital to develop a general strategy to fabricate the LDHs with special morphology and structure.Herein,we designed a unified sodium oleate（NaOA）assisted two-step two-phase solvothermal（TTS）method to fabricate LDH nanorings with different element compositions.We screened samples with optimal electrochemical or photocatalysis performance by adjusting the amount of the metal salt added in the second step.The most important thing was,in present work,we proposed the formation mechanism of LDH nanorings and theoretically demonstrated feasibility of this general strategy.The formation mechanism of nonorings can be ascribed to synergic effects of dissolution-recrystallization process and Ostwald ripening process,which promoted by solubility and oleate ions.Main research content were listed as follows:（1）We synthesized the CoAlNi LDH nanorings and discussed the influence of content of Ni on the supercapacitor performance.According to the electrochemical test of samples,CoAlNi LDH nanorings with different Ni content for the electrodes of supercapacitors showed structure-dependent performance.Additionally,electrochemical test results showed CoAlNi LDH nanorings with Ni content equaling to 3 mmol possessed the biggest interlayer distance（46.5（?））and capacitance(1339.6F g^-1 at current density of 1 A g^-1).To further explore the practical application of CoAlNi-LDH-NR electrode,an asymmetric supercapacitor（ASC）was assembled.The capacitance of the ASC device reach to 141 F g^-1 and the retention rate of it can keep at82%over 3000 cycles at current density of 2 A g^-1).（2）We synthesized the MgAlNi LDH nanorings and discussed the influence of content of Ni on the photocatalytic reduction of CO₂.The experimental results showed that when the reactant amount of Ni was equal to 3 mmol,the sample possessed the biggest interlayer distance（46.0（?））and had higher light absorption and effective charge separation efficiency.The rate of CO evolution reached a highest rate of 2.13μmol h^-1g^-1.（3）We synthesized the MgAlCo LDH nanorings and discussed the influence of content of Co on the photocatalytic reduction of CO₂.The experimental results showed that when the reactant amount of Co was equal to 3 mmol,the band gap of sample was 1.98eV and was of the best charge separation efficiency.The rate of CO evolution reached a highest rate of 1.29μmol h^-1 g^-1.