Multiple active cobalt species embedded in microporous nitrogen-doped carbon network for the selective production of hydrogen peroxide.

To obtain excellent electrocatalysts for improving H2O2 yield and selectivity, we formulated a novel method for embedding cobalt catalytic active sites in porous two-dimensional nitrogen-doped carbon network (CNy) network and employed them as excellent two-electron oxygen reduction reaction (2e--ORR) electrocatalysts. The polymeric cobalt-based metal-organic framework (polyCo-MOF) and melamine-cyanuric acid-complex (MCA) hybrid (denoted as polyCo-MOF@MCA) was used as a precursor for preparing a series of electrocatalysts comprising multiple active sites such as metallic Co, CoOx, or Co-N, which are homogeneously embedded in the porous two-dimensional CNy network through pyrolysis at high temperatures (600 °C, 700 °C, and 800 °C) under N2 atmosphere. The obtained CoOx/Co@CNy,700 hybrid by pyrolyzing polyCo-MOF@MCA at 700 °C displayed remarkably high H2O2 production and large selectivity in an alkaline solution. The possible catalytic mechanism of CoOx/Co@CNy,700 toward 2e--ORR was identified by determining the catalytic kinetics and control experiments. The cathode assembled with the CoOx/Co@CNy,700 hybrid showed the maximum H2O2 production of 405 mmol L-1gcat.-1h-1 with a high Faradaic efficiency of 88.9 % at 0.65 V. The present work demonstrated a novel strategy for identifying excellent electrocatalysts with homogeneously dispersed multiple active sites and high production and selectivity for H2O2 synthesis, extending the applications of porous organic frameworks to the field of clean energy.

Multiple cobalt active sites evenly embedded in mesoporous carbon nanospheres derived from a polymer-metal-organic framework: efficient removal and photodegradation of malachite green.

A series of robust photocatalysts of mesoporous carbon nanospheres embedded with multiple cobalt active sites (Co/Co x O y @mC) have been constructed for efficient removal and photodegradation of malachite green (MG). Here, a cobalt-based polymeric-metal-organic framework (polyMOF(Co)) was constructed by using a polyether ligand containing 1,4-benzenedicarboxylic acid units. Afterward, polyMOF(Co) was calcined into a series of Co/Co x O y @mC hybrids at diverse high temperatures (400, 600, and 800 °C) under a N2 atmosphere. Therefore, Co coordination centers were transformed into various active sites such as Co, CoO, and Co3O4, which were embedded within the mesoporous carbon network derived from the polymeric skeleton. Considering the even distribution of Co-related active species and high porosity inherited from polyMOF(Co), the constructed Co/Co x O y @mC hybrid obtained at 600 °C illustrated higher removal ability (79%) with a maximum adsorption capacity of 314 mg g-1 within 120 min and better photodegradation performance (degradation rate of 95%) toward MG than those of the other photocatalysts obtained at 400 and 800 °C. Moreover, the possible photocatalytic reaction mechanisms, including the transfer behavior of charge carriers, generation of reactive species, and intermediate degradation of products, were provided. The present work showed an alternative strategy for the feasible and efficient preparation of photocatalysts based on MOFs.

Universal biosensing platform based on polyMn-MOF nanosheets for efficient analysis of foodborne pathogens from diverse foodstuffs.

A universal electrochemical aptasensing strategy was developed for sensitive detection of various pathogenic bacteria (such as Staphylococcus aureus, Escherichia coli O157:H7, and Salmonella enterica) that commonly existed in food products. Diverse categories of pathogenic bacterium-targeting aptamers were separately immobilized over the polyMOF, which was prepared using the polyether polymer ligand containing 1,4-benzenedicarboxylic acid (polyH2bdc) units as building block, 4,4'-bipyridine as co-ligand, polyvinyl pyrrolidone as structural regulator, and MnCl2 as metal centers (represented by polyMn-MOF). The developed polyMn-MOF-based aptasensor illustrated ultralow limits of detection for three kinds of foodborne pathogens (2.6, 1.5, and 3.5 CFU mL-1 for SE, S. aureus, and E. coli, respectively) in a wide linear range of 10 - 1 × 108 CFU mL-1 of pathogenic bacteria concentration by differential pulse voltammetry, accompanying with high selectivity, good stability, and superior reproducibility. Considering these advantages, the fabricated polyMOF-based aptasensor demonstrated wide applications in food safety and analysis and other biosensing fields.

Electrochemical aptasensing strategy based on a multivariate polymertitanium-metal-organic framework for zearalenone analysis.

An electrochemical aptasensing strategy was developed with a novel bioplatform based on a multivariate titanium metal-organic framework, i.e. MTV polyMOF(Ti), to detect zearalenone (ZEN). MTV polyMOF(Ti) was prepared by using mixed linkers of polyether polymer (pbdc-xa or L8, pbdc = poly(1,4-benzenedicarboxylate) and 1,4-benzenedicarboxylic acid (H2bdc or L0) as well as tetrabutyl titanate as nodes (MTV polyMOF(Ti)-L8,0). Compared with Ti-MOFs synthesized by using the single ligand of L8 or L0, MTV polyMOF(Ti)-L8,0 shows more porous structure assembled with multilayered nanosheets. In light of the improved electrochemical activity and strong bioaffinity to the aptamer, the aptasensor based on MTV polyMOF(Ti)-L8,0 shows excellent performance for detecting ZEN with the ultralow detection limit at fg mL-1 level in the linear range of 10 fg mL-1 to 10 ng mL-1, along with good selectivity, reproducibility, stability, regenerability, and applicability.