Ecosystem services value assessment and forecasting using integrated machine learning algorithm and CA-Markov model: an empirical investigation of an Asian megacity

The ecosystem services in an area are quite dependent on its ambient land use and land cover (LULC) attributes. Here we assess the spatio-temporal distribution of Ecosystem Services Value (ESV) for the years 1990, 2000, 2010, 2020, based on the then existing LULC aspects of the Kolkata Urban Agglomeration in eastern India. Further, these are simulated for 2030, 2040 and 2050 to determine the future potential ESV. The respective LULC layers were extracted from Landsat images using the support vector machine method and future projections were done using Markov Chain-Cellular Automata models. Results reveal that all LULC aspects are likely to significantly decrease except built-up tracts. The available ESV shall concomitantly decline by 29.7%, especially due to wetland loss. The ESV patterns also showed strong spatial correlation/clustering, with higher ESV patches locating along rivers/wetlands. These results can better inform management of high-value EVS components for sustaining/improving the urban environmental quality

Binder-Free Growth of Nickel-Doped Iron Sulfide on Nickel Foam via Electrochemical Deposition for Electrocatalytic Water Splitting

Iron–sulfur-based materials are advantageous for electrocatalytic activity owing to their high natural abundance and lesser toxicity. A few investigations on the hydrogen evolution reaction (HER) catalyzing activity of Fe–S materials were performed. However, the oxygen evolution reaction (OER) catalyzing activity or overall water splitting activity of Fe–S materials has not been studied extensively till date. Another technical aspect that suppresses the activity of the electrocatalyst is related to the usage of polymeric binders for electrode fabrication. Keeping these aspects in mind, iron sulfide was directly electrodeposited on nickel foam by varying the deposition potentials and duration of deposition. Ni-doped O-incorporated iron sulfide having the FeS2 lattice domains was obtained as the deposition product. The morphology, electronic structure, and charge carrier density in the valence band of the electrodeposits changed with the change in duration of electrodeposition, which in turn modulated the electrocatalytic activity. The electrode fabricated at −0.9 V potential after 30 min was found to be superior toward HER and OER. The electrodeposit obtained after 45 min showed comparable HER catalyzing activity. An asymmetric electrolyzer constructed with these electrodes showed a comparable water splitting activity to that of the RuO2(+)||Pt/C(−) electrolyzer and also surpassed its activity at higher potential

Urban wetland fragmentation and ecosystem service assessment using integrated machine learning algorithm and spatial landscape analysis

Dynamics of ecosystem service value (ESV) of various wetlands has been assessed by researchers globally. But the impact of spatio-temporal variation of landscape metrics on ESV in the lower Gangetic plains has not been examined, fully. The present work has established linkages between landscape metrics and ESV in Kolkata urban agglomeration using support vector machine and multivariate regression analysis. Result indicates that wetland area has been reduced by 5.26%, 13.67% and 9.03% during the periods 1990–2000, 2000–2010 and 2010–2020, respectively and the ESV contributed by wetlands has been decreased by $131428,$323674 and $184649, respectively during the same period at an annual rate of 0.85%. Number of patches, mean patch area and edge density are the main determinants of wetland fragmentation and decreased by 44.12%, 10.23% and 8.65%, respectively during the last three decades. A wetland restoration strategy based on dynamic restoration, reactive restoration and wetland creation for the study area has been formulated, which can guide for sustainable management of wetland resources in Kolkata urban agglomeration

Assessment of wetland health dynamics: Comparing fuzzy- AHP and composite indexing methods in an urban agglomeration in east India

In Kolkata metropolitan area population growth, built-up land expansion, and infrastructure development shrinkages wetland area and degrades wetland health. Wetland health index was computed using composite-indexing (CI) and fuzzy-AHP (FA) models. Both CI and FA models performed well to assess wetland health where FA outperformed CI. The area under curve value ranges from 0.728 to 0.780 for CI and 0.745 to 0.855 for FA model. During the last two decades, the growth rate of built-up land was 1.86% per year and the shrinkage rate of wetland was 1.56% per year. The spatial coverage of excellent wetland area was decreased from 52.46% to 43.11% over last two decades, but the area under very poor wetlands have increased from 5.55% to 9.62%. Due to wetland health degradation, ecosystem service value was decreased by 23.50% over the last two decades. Wetland health has direct relationship with wetland size, which needs further research

Understanding the Synergistic Effect in Oxygen Evolution Reaction Catalysis from Chemical Kinetics Point of View: An Iron Oxide/Nickel Oxide Case Study

The Oxygen Evolution reaction (OER) is still an enigmatic process, and a few research efforts have been deployed to understand its thermodynamic aspects. However, to date, no significant attention has been given to understand the chemical kinetics of the OER. Herein, the oxides of nickel and iron, and their heterostructure were chosen for the investigation. The electrocatalytic activity was found to augment synergistically when a heterostructure was formed between iron oxide and nickel oxide. The metal oxide catalyzed OER was an entropy-driven process and followed the peroxide linkage formation pathway. The rate-determining step was found to be different for the reactions catalyzed by different oxides. For the first time, Distribution of relaxation time (DRT) plots were utilized to study the chemical kinetics of OER, and the inference obtained from this analysis agreed well with the reaction mechanism. The kinetic barrier for the charge transfer process was found to decrease, and the surface group formation attained a moderate value after the heterostructure formation. These aspects had been the key player behind the synergistic increment in OER catalytic activity of the heterostructure. This investigation will lead a new pathway towards the development of strategies to understand the kinetics of an electrochemical reaction

Tribological behavior of dodecylamine functionalized graphene nanosheets dispersed engine oil nanolubricants

The present study investigates the tribological properties of nanolubricants dispersed with dodecylamine functionalized graphene (DAG) in commercial engine oil. Standard techniques were used to determine the morphology of the DAG and the worn surfaces. The tribological properties of the nanolubricants were measured using UMT-2 tribotester with an in-house attachment developed for measuring the friction of liquid lubricants. The nanolubricants were observed to reduce the coefficient of friction (COF) by a maximum ∼40% in comparison to base engine oil. Parameters including the concentration, load and sliding velocity were found to influence the variation of COF considerably. Characterization of the wear tracks by EDX and XPS suggests the formation of a tribo-film as the plausible mechanism which lowers the COF in case of the nanolubricants

Effect of Ion Diffusion in Cobalt Molybdenum Bimetallic Sulfide toward Electrocatalytic Water Splitting

The electrocatalyst comprising two different metal atoms is found suitable for overall water splitting in alkaline medium. Hydrothermal synthesis is an extensively used technique for the synthesis of various metal sulfides. Time-dependent diffusion of the constituting ions during hydrothermal synthesis can affect the crystal and electronic structure of the product, which in turn would modulate its electrocatalytic activity. Herein, cobalt molybdenum bimetallic sulfide was prepared via hydrothermal method after varying the duration of reaction. The change in crystal structure, amount of Co–S–Mo moiety, and electronic structure of the synthesized materials were thoroughly investigated using different analytical techniques. These changes modulated the charge transfer at the electrode–electrolyte interface, as evidenced by electrochemical impedance spectroscopy. The Tafel plots for the prepared materials were investigated considering a less explored approach and it was found that different materials facilitated different electrocatalytic pathways. The product obtained after 12 h reaction showed superior catalytic activity in comparison to the products obtained from 4, 8, and 16 h reaction, and it surpassed the overall water splitting activity of the RuO2–Pt/C couple. This study demonstrated the ion diffusion within the bimetallic sulfide during hydrothermal synthesis and change in its electrocatalytic activity due to ion diffusion

Effect of the Solvent Ratio (Ethylene Glycol/Water) on the Preparation of an Iron Sulfide Electrocatalyst and Its Activity towards Overall Water Splitting

The polyol method is an efficient procedure for metal sulfide preparation where polyol not only acts as a solvent but also as reducing and morphology‐modulating agent. Herein, iron sulfide particles were prepared via a modified polyol method by changing the ethylene glycol (EG) : water (H2O) ratio in the mixed solvent. Analytical techniques and electronic microscopy studies confirmed that the change in EG : H2O ratio modulated the crystal structure, morphology, and electronic structure of the prepared iron sulfide particles. The electrocatalytic activity of iron sulfide changed owing to these modulations. EG helped in the formation of a sheet‐like structure – a morphology that favours a higher accessibility to the catalytically active sites. As evidenced form electrochemical impedance studies, an increased electron density near the Fermi level, a faster substrate adsorption‐desorption rate at the active sites, and a faster charge transfer at the electrode‐electrolyte interface were the key factors for the amplification in catalytic activity. The prepared iron sulfide particles showed an overall water splitting efficiency that is comparable to that of the state‐of‐the‐art RuO2‐Pt/C couple in alkaline medium. This study shows the potential of the polyol method in the preparation and catalytic‐activity modulation of Fe−S‐based electrocatalysts

Cobalt Sulfide/Nickel Sulfide Heterostructure Directly Grown on Nickel Foam: An Efficient and Durable Electrocatalyst for Overall Water Splitting Application

Fabrication of high-performance noble-metal-free bifunctional electrocatalysts for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in water is a promising strategy toward future carbon-neutral economy. Herein, a one-pot hydrothermal synthesis of cobalt sulfide/nickel sulfide heterostructure supported by nickel foam (CoSx/Ni3S2@NF) was performed. The Ni foam acted as the three-dimensional conducting substrate as well as the source of nickel for Ni3S2. The formation of CoSx/Ni3S2@NF was confirmed by X-ray diffraction and X-ray photoelectron spectroscopy. The formation of CoSx/Ni3S2@NF facilitated easy charge transport and showed synergistic electrocatalytic effect toward HER, OER, and overall water splitting in alkaline medium. Remarkably, CoSx/Ni3S2@NF showed catalytic activity comparable with that of benchmarking electrocatalysts Pt/C and RuO2. For CoSx/Ni3S2@NF, overpotentials of 204 and 280 mV were required to achieve current densities of 10 and 20 mA cm–2 for HER and OER, respectively, in 1.0 M KOH solution. A two-electrode system was formulated for overall water splitting reaction, which showed current densities of 10 and 50 mA cm–2 at 1.572 and 1.684 V, respectively. The prepared catalyst exhibited excellent durability in HER and OER catalyzing conditions and also in overall water splitting operation. Therefore, CoSx/Ni3S2@NF could be a promising noble-metal-free electrocatalyst for overall water splitting application

Optimization of active surface area of flower like MoS2 using V-doping towards enhanced hydrogen evolution reaction in acidic and basic medium

Two dimensional layered transition metal dichalcogenides (TMDS) have immense potential as inexpensive electro-catalyst for hydrogen evolution reaction (HER). Modification of crystal and electronic structure is a promising strategy to enhance the catalytic performance of TMDS. Herein, a colloquial solvothermal method was used to prepare the vanadium (V) doped MoS2 (VMSd). The structural, morphological and chemical analysis confirmed the formation of highly pure and uniform VMSd nanoflower. Tuning of V content in MoS2 successively improved its catalytic activity towards hydrogen evolution reaction (HER). As, evident from the polarization curve, the VMSd required low overpotential of 194 and 206 mV to achieve benchmarking current density of 10 mA cm−2 in acidic and basic medium, respectively. Mott-Schottky analysis suggested that the flat band potential of MoS2 differed upon V-doping, resulting in alteration of charge transfer ability at the electrode-electrolyte interface. The Fermi level shifted towards the conduction band with optimized V-doping and the band structure got modified effectively