Temperature Dependent Characteristics of Activated Carbons from Walnut Shells for Improved Supercapacitor Performance

Activated carbons (ACs) have been prepared from chemical treatment of walnut shells (WS) precursor at various temperatures (400‒800 °C) by using phosphoric acid (H3PO4) as activating agent. Influence of activation temperature on the porosity development and capacitive properties of resulting carbons was investigated. Thermal post-treatment of carbons previously activated at moderate temperature, e.g. 400 °C allowed further structural and porosity modification. Then, these carbons were investigated by scanning electron microscopy, Raman spectroscopy, energydispersive X-ray spectroscopy, electrochemical techniques and low temperature nitrogen adsorption exhibiting high BET specific surface area of approximately 2100 m2 g-1 and a total pore volume up to 1.3 cm3 g-1. Carbon material obtained through activation by H3PO4 at 400 °C and post-treated at 800 °C was used to make electrodes which were implemented to realize AC/AC capacitor using 1 mol L-1 Li2SO4. The electrochemical capacitor demonstrated high capacitance of 123 F g-1 per mass of one electrode, reduced cell resistance and stable capacitance for 5000 galvanostatic charge/discharge cycles at 1.0 A g-1

REVISITING THE CARBON MESOPORE CONTRIBUTION TOWARDS IMPROVED PERFORMANCE OF IONIC LIQUID–BASED EDLCS AT SUB ZERO TEMPERATURES

The important role of mesopores has been investigated in electric double-layer capacitors (EDLCs) operating from 24 °C down to−40 °C by using two in-house synthesized carbons with hierarchical porosity. These carbons were prepared from colloidal nanoparticles of SiO2 as the template and d-glucose as the carbon source. A decrease in the average diameter of the nanoparticles from 12 to 8 nm results in increased surface area and ofers a perfect match between ions of binary mixture of imidazolium-based fuorinated ionic liquids and the pores of carbon. Short-range graphene layers produced with 8-nm silica nanoparticles lead to the creation of transport channels which better accommodate ions. We explain these fndings per coulombic interactions among the ions and between the pore wall and the ionic species under confnement and electrochemical polarization conditions. Further, it is shown that a microporous carbon (another in-house produced rice-husk carbon SBET=1800 m2 ∙g−1) performs better than hierarchical carbons at room temperature; however, thanks to the large fraction of mesopores, the latter exhibit far higher capacitance down to−40 °C. While the ordering of ions in confnement is more critical at room temperature and dictated by the micropores, low temperature performance of supercapacitors is determined by the mesopores that provide channels for facile ion movement and keep the bulk ionic liquid–like properties

Экспериментальное исследование закономерностей электрохимической сорбции/десорбции ионов золота (III)

For the Republic of Kazakhstan as a country with developed mining and processing sectors, a topical issue is to develop the areas of knowledge aimed at improving and refining methods and technologies for comprehensive mineral processing including for the more complete extraction of precious metals. The necessity of these studies is determined by the high loss of precious metals during their processing and separation and the need to improve the process of their concentration. Advances in the field of carbon nanomaterials offer great prospects for improving existing technologies for the precious metal extraction from waste solutions and pulps. This paper covers the comprehensive studies into the influence of the solution flow rates, pH and the presence of ions of other metals on the extraction of gold on a carbon nanostructured material consisting of rice husk with its further regeneration and reuse. It was found that the highest gold (III) ion recovery is observed at pH ~ 2. The gold recovery efficiency was studied in the combined presence of copper, nickel and silver. The dependence of the electrochemical reduction sorption of gold on the flow rate of solutions was investigated. It was found that the optimal solution flow rate is 10 ml/min. The sorption capacity of a sorbent based on carbonized rice husk was calculated. The investigation of electrochemical sorption/desorption of gold (III) ions showed that the desorption process runs better in an acetone + water + NaOH mixture with a desorption degree of 96 %. This demonstrates the possibility of regenerating the electrode carbon material for reuse. The results obtained can be used to optimize the processes of extraction of precious metals from their solutions.Для Республики Казахстан, как для страны с развитыми добывающими и перерабатывающими отраслями промышленности, актуальным направлением является развитие областей знаний, направленных на улучшение и совершенствование методов и технологий комплексной переработки сырья, в том числе для более полного извлечения благородных металлов. Основанием необходимости проведения этих исследований являются высокие потери благородных металлов при их переработке и выделении, а также совершенствование процесса их концентрирования. Достижения в области углеродных наноматериалов открывают большие перспективы для модернизации существующих технологий извлечения благородных металлов из отходящих растворов и пульп. В настоящей работе проведены комплексные исследования влияния скорости потока растворов, величины pH и присутствия ионов других металлов на извлечение золота на углеродном наноструктурированном материале из рисовой шелухи с дальнейшей его регенерацией и повторным использованием. Выявлено, что наивысшая степень извлечения ионов золота (III) наблюдается при pH ~ 2. Исследована эффективность извлечения золота при совместном присутствии меди, никеля и серебра. Рассмотрена зависимость электрохимической восстановительной сорбции золота от скорости потока растворов, оптимальная величина которой составила 10 мл/мин. Рассчитана сорбционная емкость сорбента на основе карбонизованной рисовой шелухи. Исследование электрохимической сорбции/десорбции ионов золота (III) показало, что процесс десорбции лучше протекает в смеси ацетон + вода + NaOH. При этом степень десорбции достигает 96 %, что свидетельствует о возможности регенерации углеродного материала электрода для повторного применения. Полученные результаты могут быть применены для оптимизации процессов извлечения благородных металлов из их растворов