Influences of graphene oxide support on the electrochemical performances of graphene oxide-MnO2 nanocomposites

MnO2 supported on graphene oxide (GO) made from different graphite materials has been synthesized and further investigated as electrode materials for supercapacitors. The structure and morphology of MnO2-GO nanocomposites are characterized by X-ray diffraction, X-ray photoemission spectroscopy, scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, and Nitrogen adsorption-desorption. As demonstrated, the GO fabricated from commercial expanded graphite (denoted as GO(1)) possesses more functional groups and larger interplane gap compared to the GO from commercial graphite powder (denoted as GO(2)). The surface area and functionalities of GO have significant effects on the morphology and electrochemical activity of MnO2, which lead to the fact that the loading amount of MnO2 on GO(1) is much higher than that on GO(2). Elemental analysis performed via inductively coupled plasma optical emission spectroscopy confirmed higher amounts of MnO2 loading on GO(1). As the electrode of supercapacitor, MnO2-GO(1) nanocomposites show larger capacitance (307.7 F g-1) and better electrochemical activity than MnO2-GO(2) possibly due to the high loading, good uniformity, and homogeneous distribution of MnO2 on GO(1) support

A survey of Earth-abundant metal oxides as oxygen evolution electrocatalysts in acidic media (pH < 1)

This article is part of the themed collection: Hydrogen productionElectrolytic hydrogen appears as one of the most promising options to store renewable energy. In this water splitting process, the sluggish kinetics of the 4-electron oxygen evolution reaction (OER) with its high overpotentials have been widely regarded as the bottleneck to facilitate a fast, energy-efficient process. In alkaline media, numerous earth-abundant metal oxides are efficient OER catalysts, stabilized by the high concentration of hydroxide anions in the electrolyte. However, under acidic conditions, where the hydrogen evolution reaction (HER) is technologically preferred, only noble metal-based oxides (RuO2 and IrO2) are suitable OER catalysts, putting into question the scalability to wide-spread applications due to their scarcity and high cost. Most earth abundant metal oxides dissolve at high proton concentrations. A promising strategy to avoid this drawback consists of incorporating these catalysts into partially hydrophobic composite electrodes. Following this strategy, we have been able to conduct an extensive survey of the activity and stability of mono-, bi- and trimetallic earth-abundant transition metal oxides during the electrocatalytic OER under strongly acidic conditions. Our results confirm the general validity of the strategy by using a hydrophobic electrode to confer high stability to common metal oxides under these harsh conditions. Among all OER catalysts investigated, we found that simple manganese oxides appeared as the most active also exhibiting high, long-term stability. In particular, the stability of Mn2O3 oxide in the OER in acidic media was well confirmed by post-electrolysis characterization data.The authors are thankful for the support from MCIN/AEI/10.13039/501100011033/ and “ERDF A way of making Europe” through projects RED2022-134508-T (CAT&SCALE), PID2021-124796OB-I00 and PID2020-116093RB-C43&C44 funded by MCIN/AEI/10.13039/501100011033; from the Generalitat de Catalunya (2021SGR1154 and 2021SGR00457), and from the Basque Government (IT-1591-22). S.B. acknowledges RYC-2017-21931 funded via MCIN/AEI/10.13039/501100011033 and by ESF Investing in your future and UPV/EHU project EHUrOPE19/01. ICIQ and ICN2 are supported by the Ministerio de Ciencia e Innovación through the Severo Ochoa Excellence Accreditations CEX2019-000925-S (MCIN/AEI) and CEX2021-001214-S; and by the CERCA Programme/Generalitat de Catalunya. J.Y. thanks the China Scholarship Council (CSC) for predoctoral fellowships (File No. 201806270234). J.R. acknowledges the Czech Science Foundation and funding from PIF outgoing project number 22-18079O. M.C.S. has received funding from the European Union's Horizon 2020 research and innovation programme under Marie Skodowska-Curie grant 754510 (PROBIST) and the Severo Ochoa programme. M.C.S. is also thankful for the funding from the postdoctoral fellowship Juan de la Cierva Incorporation from MICINN (JCI-2019) and the Severo Ochoa programme. This study is part of the Advanced Materials programme and was supported by MCIN with funding from the European Union NextGenerationEU (PRTR-C17.I1) and the Generalitat de Catalunya.With funding from the Spanish government through the "Severo Ochoa Centre of Excellence" accreditation (CEX2019-000925-S).With funding from the Spanish government through the "Severo Ochoa Centre of Excellence" accreditation (CEX2021-001214-S).Peer reviewe

Chemical analysis and statistical study on the composition of airborne particulate matter (PM2.5 and PM10 ), aerosols (PM2.5 ) inorganic trace gases and precipitation in Singapore between 2009 – 2012

Abstract At a Nanyang Technological University (NTU) rooftop sampling site, airborne particulates were sampled in two different sizes of 10 and 2.5 µm between October 2009 to December 2011. Airborne particulate matter samples were acid digested using a microwave system in closed vessels. The amount of acids, power setting and digestion times were optimized in order to achieve an efficient digestion. An inductively coupled plasma mass spectrometry (ICP-MS) method was developed for the determination of the elemental composition of airborne particulate matter. The developed microwave procedure and ICP-MS method were tested with NIST Standard Reference Material 2783 Urban Particulate Matter based on the recovery test. It was found that major elements were present in the airborne particulate matter with high concentrations (µg m-3) in the order of Na > Ca > Al > K > Mg > Zn > Fe. The enrichment factor (EF) was used as a means to determine whether the elements originated from natural or anthropogenic sources. Their main sources were likely to be anthropogenic, for instance vehicular and industrial emissions. PMF applied to the 54-variable model apportioned the airborne particulate matter into several sources including sea salt, crustal and windblown dust, road dust, vehicular emissions, refineries and chemical industries, electronics and semiconductors, high temperature operations and construction.DOCTOR OF PHILOSOPHY (SPMS

Nano/Microrobots Line Up for Gastrointestinal Tract Diseases: Targeted Delivery, Therapy, and Prevention

Nano/microrobots (NMRs) are tiny devices that can convert energy into motion and operate at nano/microscales.54 Especially in biomedical research, NMRs have received much attention over the past twenty years because of their excellent capabilities and great potential in various applications, including on-demand drug delivery, gene and cell transport, and precise microsurgery. Reports published in recent years show that synthetic nano/microrobots have promising potential to function in the gastrointestinal (GI) region, particularly in terms of drug delivery. These tiny robots were able to be designed in such a way that they propel in their surroundings (biological media) with high speed, load cargo (drug) efficiently, transport it safely, and release upon request successfully. Their propulsion, retention, distribution, and toxicity in the GI tract of mice has been evaluated. The results envisage that such nano/microrobots can be further modified and developed as a new-generation treatment of GI tract diseases. In this minireview, we focus on the functionality of micro/nanorobots as a biomedical treatment system for stomach/intestinal diseases. We review the research progress from the first in vivo report in December 2014 to the latest in August 2021. Then, we discuss the treatment difficulties and challenges in vivo application (in general) and possible future development routes

Graphene oxides prepared by Hummers’, Hofmann’s, and Staudenmaier’s methods : dramatic influences on heavy-metal-ion adsorption

Graphene oxide (GO), an up-and-coming material rich in oxygenated groups, shows much promise in pollution management. GO is synthesised using several synthetic routes, and the adsorption behaviour of GO is investigated to establish its ability to remove the heavy-metal pollutants of lead and cadmium ions. The GO is synthesised by Hummers’ (HU), Hofmann’s (HO) and Staudenmaier’s (ST) methodologies. Characterisation of GO is performed before and after adsorption experiments to investigate the structure–function relationship by using Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy. Scanning electron microscopy coupled with elemental detection spectroscopy is used to investigate morphological changes and heavy-metal content in the adsorbed GO. The filtrate, collected after adsorption, is analysed by inductively coupled plasma mass spectrometry, through which the efficiency and adsorption capacity of each GO for heavy-metal-ion removal is obtained. Spectroscopic analysis and characterisation reveal that the three types of GO have different compositions of oxygenated carbon functionalities. The trend in the affinity towards both PbII and CdII is HU GO>HO GO>ST GO. A direct correlation between the number of carboxyl groups present and the amount of heavy-metal ions adsorbed is established. The highest efficiency and highest adsorption capacity of heavy-metal ions is achieved with HU, in which the relative abundance of carboxyl groups is highest. The embedded systematic study reveals that carboxyl groups are the principal functionality responsible for heavy-metal-ion removal in GO. The choice of synthesis methodology for GO has a profound influence on heavy-metal-ion adsorption. A further enrichment of the carboxyl groups in GO will serve to enhance the role of GO as an adsorbent for environmental clean-up

Corrosion due to ageing influences the performance of tubular platinum microrobots

Autonomous self-propelled nano and microrobots are in the forefront of materials research. The micromachines are typically prepared in batches, stored and subsequently used. We show here that the storage of platinum tubular catalytic microrobots in water causes their corrosion which results in their lower mobility and performance. This has important implications for the construction and storage of these autonomous micromotors.MOE (Min. of Education, S’pore)Accepted versio

Annual air pollution caused by the Hungry Ghost Festival

Burning of joss paper and incense is still a very common traditional custom in countries with a majority Chinese population. The Hungry Ghost Festival which is celebrated in the 7 month of the Chinese calendar is one of the events where joss paper and incense are burned as offerings. This study investigates the impact of the Ghost Month Festival (open burning event) on air quality by analysis of the chemical composition of particulate matter (PM) and rainwater samples collected during this event, compared with data collected throughout the year, as well as bottom ash samples from burning the original joss paper and incense. The results showed that the change in the chemical composition of the rainwater and PM2.5 (PM ≤ 2.5 μm) atmospheric samples could be correlated directly with burning events during this festival, with many elements increasing between 18% and 60% during August and September compared to the yearly mean concentrations. The order of percentage increase in elemental composition (in rain water and PM2.5) during the Hungry Ghost Festival is as follows: Zn > Ca > K > Mg > Fe > Al > Na ∼ Mn ∼ Ti ∼ V > Cu > As > Ni > Co > Cd > Cr > Pb. The chemical composition of the original source materials (joss paper and incense for combustion) and their associated bottom ash were analysed to explain the impact of burning on air quality.MOE (Min. of Education, S’pore)Published versio

Metallic impurities in graphenes prepared from graphite can dramatically influence their properties

All at C? Graphenes prepared by the top-down exfoliation of graphite are shown to contain metallic impurities (see scheme, metal impurities shown as black dots). These impurities may dominate their properties and can have a negative influence on their potential applications

Mercury isotopes of atmospheric particle bound mercury for source apportionment study in urban Kolkata, India

Abstract The particle bound mercury (PBM) in urban-industrial areas is mainly of anthropogenic origin, and is derived from two principal sources: Hg bound to particulate matter directly emitted by industries and power generation plants, and adsorption of gaseous elemental mercury (GEM) and gaseous oxidized mercury (GOM) on air particulates from gas or aqueous phases. Here, we measured the Hg isotope composition of PBM in PM10 samples collected from three locations, a traffic junction, a waste incineration site and an industrial site in Kolkata, the largest metropolis in Eastern India. Sampling was carried out in winter and monsoon seasons between 2013–2015. The objective was to understand whether the isotope composition of the PBM represents source composition. The PBM collected from the waste burning site showed little mass independent fractionation (MIF) (Δ199Hg = +0.12 to -0.11‰), similar to the signature in liquid Hg and Hg ores around the world with no seasonal variations. Samples from the industrial site showed mostly negative MDF and MIF (δ202Hg = -1.34 to -3.48 ‰ and Δ199Hg = +0.01 to -0.31‰). The MDF is consistent with PBM generated by coal combustion however, the MIF is 0.15‰ more negative compared to the Hg isotope ratios in Indian coals. The traffic junction PBM is probably not produced in situ, but has travelled some distances from nearby industrial sources. The longer residence time of this PBM in the atmosphere has resulted in-aerosol aqueous photoreduction. Thus, the MIF displays a larger range (Δ199Hg = +0.33 to -0.30‰) compared to the signature from the other sites and with more positive values in the humid monsoon season. Different Hg isotopic signature of PBM in the three different sampling locations within the same city indicates that both source and post emission atmospheric transformations play important roles in determining isotopic signature of PBM