RSC Advances

Boyadzhieva, Tanya; Koleva, Violeta; Kukeva, Rosica; Nihtianova, Diana; Harizanova, Sonya; Stoyanova, Radostina

doi: 10.1039/d0ra05698gpmid: 35521091

Sodium manganese phospho-olivine, NaMnPO4, is considered to be a higher-voltage alternative to the presently used iron-based electrode material, NaFePO4, for sodium ion batteries. Irrespective of this advantage, the electrochemical performance of NaMnPO4 is still far from what is desired. Herein we provide the first report on the storage performance of NaMnPO4 having a structure modified by Mg2+ substitution. The Mg-substituted phospho-olivines are prepared on the basis of ionic exchange reactions involving the participation of Mg-substituted KMnPO4·H2O dittmarites as structural template. Furthermore, the phosphate particles were covered with a thin layer (up to 5 nm) of activated carbon through ball-milling. The storage performance of phospho-olivines is analyzed in sodium and lithium half-ion cells, as well as in full-ion cells versus bio-mass derived activated carbon and spinel Li4Ti5O12 as anodes. The compatibility of phospho-olivines with electrolytes is assessed by utilization of several types of lithium and sodium carbonate-based solutions. In sodium half-cell, the Mg-substituted phosphate displays a multi-phase mechanism of Na+ intercalation in case when NaTFSI-based electrolyte is used. In lithium half-cell, the high specific capacity and rate capability is achieved for phospho-olivine cycled in LiPF6-based electrolyte. This is a consequence of the occurrence of dual Li+,Na+ intercalation, which encompass nano-sized domains. The utilization of the Mg-substituted phospho-olivine in the full ion cell is demonstrated.

Li, Zhijian; Gong, Congcong; Huo, Panpan; Deng, Chunhui; Pu, Shouzhi

doi: 10.1039/d0ra04125dpmid: 35521136

Microcystin-LR (MC-LR) is a toxin released from cyanobacteria in eutrophicated water. MC-LR is the most abundant and the most toxic among microcystins. In this work, core–shell structured copper-based magnetic metal–organic framework (Fe3O4@PDA@Cu-MOFs) composites were synthesized via a solvothermal reaction and a sol–gel method. The Fe3O4@PDA@Cu-MOFs composites showed ultra-high surface area, strong magnetic response and outstanding hydrophilicity. The Fe3O4@PDA@Cu-MOFs composites combined with matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOF-MS) were used to analyse the content of MC-LR in real water samples. Under the optimised conditions, our proposed method exhibited good linearity within a concentration range of 0.05–4 μg L−1 and good detection even at low limits (0.015 μg L−1). The method was also successfully applied to analyse traces of MC-LR with quantitative recoveries for the real water samples in the range from 98.67% to 106.15%. Furthermore, it was characterized by high sensitivity, short operation time, being environmental friendly and having the ability to analyse other pollutants in the environment.

Zhou, Shunli; Zhang, Chengxi; Li, Yongxiang; Shao, Bingzhang; Luo, Yibin; Shu, Xingtian

doi: 10.1039/d0ra03762apmid: 35521147

Different amounts of SiO2 were added to the Al2O3 binders to investigate the binder effect on zeolite Y-based catalysts. The added SiO2 improved the mesopore volume and acidity of the catalysts. Characterization results showed that the catalysts' acid amount increased with increasing the SiO2 amount in the binder, which achieved maximum value when 12% SiO2 was added to the binder. The doped SiO2 in Al2O3 binders improved the Al2O3 phase transformation temperature, which is crucial for Al species to break out of the phase energy and migrate into the zeolite. The lifetime of catalyst Y-Al2O3-12SiO2 is 3.7 times higher than that of Y-Al2O3-0SiO2, and the selectivity of the target products simultaneously improved by 7 percentage point. This work should bring some inspiration to the design and application of zeolite-based catalysts.

Liang, Xiaolei; Qian, Jinmei; Liu, Yonggang; Zhang, Zhengmei; Gao, Daqiang

doi: 10.1039/d0ra04262epmid: 35521123

Large-scale application of sustainable energy devices urgently requires cost-effective electrocatalysts to overcome the sluggish kinetics related to the oxygen evolution reaction (OER) under acidic conditions. Here, we first report the highly efficient electrocatalytic characteristics of α-Fe2O3 nanorings (NRs), which exhibits prominent OER electrocatalytic activity with lower overpotential of 1.43 V at 10 mA cm−2 and great stability in 1 M HCl, surpassing the start-of-the art Ir/C electrocatalyst. The significantly optimized OER activity of the α-Fe2O3 NRs mainly attributes to the synergistic effect of the excellent electrical conductivity and a large effective active surface because of their unique nanoring structure, disordered surface, and the dynamic stability of α-Fe2O3 NRs in acidic conditions.

Yu, Wanchao; Chen, Fengjie; Wang, Yarui; Zhao, Lixia

doi: 10.1039/d0ra06299epmid: 35521112

Reactive oxygen species (ROS) play an important role in the photocatalytic degradation of pollutants and are closely related to the surface defects of a semiconductor. However, the characterization of surface defects is very complex and a deeper understanding of them remains a great challenge. In this work, a series of nano-TiO2 was synthesized and their optical properties due to surface defects were studied. The results showed that the surface oxygen vacancies on nano-TiO2 can induce chemiluminescence (CL) by luminol. The greater the number of surface oxygen vacancies, the stronger the luminescence signal, and the greater the production of reactive oxygen species. Further studies revealed that the CL intensity was positively correlated with the oxygen vacancy content on the surface of nano-TiO2. Moreover, there was also a clear correlation between the oxygen vacancies and photogenerated superoxide radicals (O2˙−) on nano-TiO2 suspensions. Therefore, a simple and rapid CL method was developed for evaluating the oxygen vacancy content and their implied ability to photogenerate O2˙− on nano-TiO2 and has great potential in distinguishing surface oxygen vacancies and judging photocatalytic performance in oxides.

Cai, Chaoyue; Fu, Jialong; Zhang, Chengyan; Wang, Cheng; Sun, Rui; Guo, Shufang; Zhang, Fan; Wang, Mingyan; Liu, Yuqing; Chen, Jun

doi: 10.1039/d0ra05199cpmid: 35521096

A flexible and free-standing 3D reduced graphene oxide@polypyrrole–polyethylene glycol (RGO@PPy–PEG) foam was developed for wearable supercapacitors. The device was fabricated sequentially, beginning with the electrodeposition of PPy in the presence of a PEG–borate on a sacrificial Ni foam template, followed by a subsequent GO wrapping and chemical reduction process. The 3D RGO@PPy–PEG foam electrode showed excellent electrochemical properties with a large specific capacitance of 415 F g−1 and excellent long-term stability (96% capacitance retention after 8000 charge–discharge cycles) in a three electrode configuration. An assembled (two-electrode configuration) symmetric supercapacitor using RGO@PPy–PEG electrodes exhibited a remarkable specific capacitance of 1019 mF cm−2 at 2 mV s−1 and 95% capacitance retention over 4000 cycles. The device exhibits extraordinary mechanical flexibility and showed negligable capacitance loss during or after 1000 bending cycles, highlighting its great potential in wearable energy devices.

Kowalkowska-Zedler, Daria; Nedelko, Natalia; Kazimierczuk, Katarzyna; Aleshkevych, Pavlo; Łyszczek, Renata; Ślawska-Waniewska, Anna; Pladzyk, Agnieszka

doi: 10.1039/d0ra06036dpmid: 35521135

Three heteroleptic complexes of Co(ii) tri-tert-butoxysilanethiolates have been synthesized with piperidine [Co{SSi(OtBu)3}2(ppd)2] 1, piperazine [Co{SSi(OtBu)3}2(NH3)]2(μ-ppz)·2CH3CN 2, and N-ethylimidazole [Co{SSi(OtBu)3}2(etim)2] 3. The complexes have been characterized by a single-crystal X-ray, revealing their tetrahedral geometry on Co(ii) coordinated by two nitrogen and two sulfur atoms. Complexes 1 and 3 are mononuclear, whereas 2 is binuclear. The spectral properties and thermal properties of 1–3 complexes were established by FTIR spectroscopy for solid samples and TGA. The magnetic properties of complexes 1, 2, and 3 have been investigated by static magnetic measurements and X-band EPR spectroscopy. These studies have shown that 1 and 3, regardless of the similarity in structure of CoN2S2 cores, demonstrate different types of local magnetic anisotropy. Magnetic investigations of 2 reveal the presence of weak antiferromagnetic intra-molecular Co(ii)–Co(ii) interactions that are strongly influenced by the local magnetic anisotropy of individual Co(ii) ions.

Kumaravel, Kandhasamy; Rajarathinam, Balakrishnan; Vasuki, Gnanasambandam

doi: 10.1039/d0ra05105epmid: 35521150

An unprecedented union of multi-component reactions to construct pyrazole- and pyranopyrazole-adorned 4H-chromene from simple reactants in water at ambient temperature is reported. This innovative tactic has integrated two distinct four-component reactions (4CRs) that occur transiently to form four new heterocycles via ten covalent bonds in a single step.

Xiao, Yuanyuan; Yi, Zijuan; Yu, Xianyong; Xiao, Fang

doi: 10.1039/d0ra05921hpmid: 35521140

The reaction employing H2O and O2 as the co-oxygen source in the catalytic synthesis of α-ketoamides is described. This copper-catalyzed reaction is carried out in a tandem manner constituted by the hydroamination of alkyne, hydration of vinyl–Cu complex and subsequent oxidation. Isotope labeling and radical capture experiments reveal that the oxygen atom of α-ketone at α-ketoamides derives from O2 and the oxygen atom of amide group originates from H2O.

Chen, Yuehan; Wang, Shuping; Li, Zhoupeng

doi: 10.1039/d0ra05143hpmid: 35521132

Pyrrole and cobalt nitrate were used as nitrogen and metal sources respectively to synthesize a dinitratobis(polypyrrole)cobalt(ii) (Co(polypyrrole)2(NO3)2) adduct as the precursor of a Co–pyrrole/MPC catalyst. Pyrrole has the capability of polymerization and coordination with Co(ii). Taking this advantage, the Co(polypyrrole)2(NO3)2 coordination can form a long-chain structure with abundant and robust Co–N bonds, contributing to significantly increased catalytic sites in the product catalyst. As a result, the obtained Co–pyrrole/MPC (MPC = macroporous carbon) catalyst exhibited high ORR catalytic activity in alkaline media and excellent performance in direct borohydride fuel cell (DBFC). A peak power density up to 325 mW cm−2 was achieved at ambient condition, outperforming the commercialized Pt/XC-72 benchmark containing 28.6 wt% Pt. The construction of long-chain coordination precursor was verified playing a key role in the electrochemical improvement of Co–pyrrole/MPC catalyst in DBFC.