Bibliometric analysis of biochar research in 2021:a critical review for development,hotspots and trend directions

As a bioproduct from the thermal decomposition of biomass,biochar has various applications in diversified field.In this study,a bibliometric analysis was conducted to visualize the current research status and trends of biochar research.A total of 5535 documents were collected from the Web of Science Core Collection and subjected to visualization analysis for the biochar field’s development in 2021 with CiteSpace software.The visual analysis results demonstrate that the number of publications expanded dramatically in 2021,and the growth trend would continue.China and USA were the most contributing countries in biochar research in terms of the number of publications.Based on the keyword co-occurrence analyses,“Biochar for toxic metal immobilization”,“Biochar-based catalyst for biofuel production”,“Biochar for global climate change mitigation”,“Biochar for salinity and drought stress amelioration”,“Biochar amendment in composting”,and“Biochar as additives in anaerobic digestion”were the main research trends and hotspots in this field in 2021.This indicates that the biochar research was multidisciplinary.Regarding the research hotspots,the employment of biochar as heterogeneous catalysts for biofuel production gained great attention in 2021.On the contrary,bioremediation using functional bacteria immobilized on biochar and biochar-assisted advanced oxidation process were well-studied but with less frequency than other topics in 2021.Furthermore,the future research was proposed for green and sustainable applications of biochar.This review provides a comprehensive overview of the research frontiers,the evolution of research hotspots,and potential future research directions in the biochar field.

Visualizing the development trend and research frontiers of biochar in 2020:a scientometric perspective

This study presents a scientometric analysis on biochar research to investigate the research status and developments as well as future trends in this field in 2020.A total of 3671 publications were retrieved from the Web of Science core collection database in 2020,which were analyzed for categories,countries,authors,and keywords.China and USA played a leading role in the research of biochar.Yong Sik Ok and Daniel C.W.Tsang were the most prolific authors in the application of biochar in agriculture,environment,and energy.Based on the keywords clustering analysis,biochar applications in“bioenergy produc-tion”,“global climate change mitigation”,“salinity and drought stress amelioration”,“organic pollutants degradation”,“heavy metals immobilization”,and“bioremediation”were the main hotspots.Biochar for salinity and drought stress amelioration became the focus in biochar area in 2020 as biochar amendment had great potential in alleviating salt-and drought-affected soils.Organic pollutants’degradation via advanced oxidation process(AOPs)represents a sustainable growing topic.Radical and non-radical pathways were summarized for AOPs.Bioremediation using functional bacteria(e.g.,heavy metal-resistant bacteria and organic pollutant-degraders)immobilized on biochar was still a research hotspot.Immobilized cells showed excellent performance in removing various contaminants by combining the advantages of highly efficient physiochemical sorption of biochar and microbial metabolisms.The review improves our understanding on scientific advances and potential future research directions in biochar research.

Visualizing the emerging trends of biochar research and applications in 2019:a scientometric analysis and review

Biochar,derived from thermal pyrolysis of biomass,has been regarded as a low-cost,sustainable and beneficial material and widely applied in agriculture,environment and energy during the last two decades.To elucidate the research status timely and future trends in biochar field,CiteSpace is used to systematically analyze the related literature retrieved from the Web of Science core collection in 2019.Based on the keywords clustering analysis,it was found that“biochar production”,“organic pollutants removal”,“heavy metals immobilization”,“bioremediation”were the main hotspots in research covering biochar.“Bioremediation”is an emerging topic and deserves extensive attention due to its highly effective and environmentally friendly treatment of pollutants.Improving the phytoremediation effect,immobilizing functional microorganisms on biochar,and using microorganisms as raw materials to produce biochar were the common methods of biochar-assisted bioremediation.While studies focused on“soil quality and plant growth”and“biochar and global climate change”decreased,investigations concentrated in the toxicity of biochar to soil biota and ruminants are sustainably growing.Research on direct and catalytic thermal pyrolysis of green waste(mainly microalgae)for biofuels(bio-oil,biodiesel,syngas,etc.)and biochar production is increasing.Converting municipal wastes(e.g.,sewage sludge,fallen leaves)into biochar through pyrolysis was a suitable treatment for municipal waste and became a popular topic in recent time.Moreover,the biochar produced from these municipal wastes exhibited excellent performance in the removal of pollutants from wastewater and soil.This review may help to identify future directions in biochar research and applications.

A scientometric review of biochar research in the past 20 years(1998-2018)

Biochar is the carbon-rich product obtained from the thermochemical conversion of biomass under oxygen-limited conditions.Biochar has attained extensive attention due to its agronomical and environmental benefits in agro-ecosystems.This work adopts the scientometric analysis method to assess the development trends of biochar research based on the literature data retrieved from the Web of Science over the period of 1998-2018.By analysing the basic characteristics of 6934 publications,we found that the number of publications grew rapidly since 2010.Based on a keyword analysis,it is concluded that scholars have had a fundamental recognition of biochar and preliminarily found that biochar application had agronomic and environmental benefits during the period of 1998-2010.The clustering results of keywords in documents published during 2011-2015 showed that the main research hotspots were“biochar production”,“biochar and global climate change”,“soil quality and plant growth”,“organic pollutants removal”,and“heavy metals immobilization”.While in 2016-2018,beside these five main research hotspots,“biochar and composting”topic had also received greater attention,indicating that biochar utilization in organic solid waste composting is the current research hotspot.Moreover,updated reactors(e.g.,microwave reactor,fixed-bed reactor,screw-feeding reactor,bubbling fluidized bed reactor,etc.)or technologies(e.g.,solar pyrolysis,Thermo-Catalytic Reforming process,liquefaction technology,etc.)applied for efficient energy production and modified biochar for environmental remediation have been extensively studied recently.The findings may help the new researchers to seize the research frontier in the biochar field.