《1 Engineering research fronts》

1 Engineering research fronts

《1.1 Trends in Top 10 engineering research fronts》

1.1 Trends in Top 10 engineering research fronts

The Top 10 engineering research fronts in the field of environmental and light textile engineering include the subfields of environmental science, meteorological science, marine science, food science, textile science, and light industry science. The citation statistics for these research fronts and the annual number of core papers for each research front between 2016 and 2021 are summarized in Tables 1.1.1 and 1.1.2, respectively.

(1)  Mechanisms of multi-media transport and transformation of new pollutants

New pollutants (or emerging pollutants) refer to newly discovered or noticed pollutants that pose risks to the ecological environment or human health, and have not yet been incorporated into management or existing management measures are insufficient to effectively prevent and control their risks. With the increasing understanding of the environmental and health hazards of chemical substances and the continuous development of environmental monitoring technology, the number of new pollutants that can be identified will continue to increase. Therefore, the development of efficient and universal analytical methods for discovering new pollutants is an important research direction in the field of new pollutant management.

The production and use of toxic and hazardous chemical substances are the main sources of new pollutants. Literature shows that higher levels of new pollutants such as environmental endocrine disruptors, antibiotics, and microplastics have been monitored successively in the atmosphere, water, and soil in some regions of China. Transfer of new pollutants among different environmental media often occurs, implying that one medium can become the pollution source for the next environmental medium, leading to differences in fate and contamination levels for new pollutants in different media. However, the migration and transformation

《Table 1.1.1》

Table 1.1.1 Top 10 engineering research fronts in environmental and light textile engineering

《Table 1.1.2》

Table 1.1.2 Annual number of core papers published for the Top 10 engineering research fronts in environmental and light textile engineering

behaviors and mechanisms of most new pollutants among multi-media are unclear, and the health risks are unclear. Around the management of new pollutants, it is necessary to further strengthen the research on environmental screening, traceability studies, environmental risk assessment and control, and research on ecological and environmental hazard mechanisms such as antibiotics and microplastics; it is also a necessary to develop with the help of mathematical methods or models to better describe the cross-media migration and transformation of new pollutants released into the atmosphere.

(2)  Treatment and resource recovery techniques for hypersaline wastewater

Hypersaline wastewater usually refers to wastewater containing dissolved salts above 3.5% (w/v). It is extensively present in the chemical industry and often contains a large number of hazardous substances such as refractory organic matters and heavy metals. In recent years, with the policies on “zero liquid discharge” and wastewater recycling vigorously promoted across the world, the development of technologies for treating and recycling hypersaline wastewater has now become a high priority in the area of water treatment.

The high-concentration inorganic ions in hypersaline wastewater would not only inhibit bacterial growth but also quench hydroxyl radicals, thus constraining organic pollutant degradation. Regarding organic pollutants removal, the current research is mostly focused on advanced oxidation technologies such as persulfate-based Fenton and spatially confined electro-catalysis. The core concept is to increase the lifetime of active species and accelerate the mass transfer of reactants for enhanced pollutants degradation. Besides, more halotolerant and halophilic bacteria have been screened and domesticated, which contributes to the removal of organic pollutants in combination with bioaugmentation technologies such as membrane bioreactors and granular sludge reactors.

Since salts and water in hypersaline wastewater are valuable resources, their separation is essential for establishing a sustainable water treatment process. Two of the important research fields are the concentration of hypersaline wastewater and the separation of mixed salts. Regarding these demands, membrane separation technologies, including nanofiltration, reverse osmosis, selective electrodialysis, and membrane distillation, have attracted much attention. To realize the industrial application of membrane technologies in the recycling of hypersaline wastewater, it’s essential to fabricate high-performance membrane materials and develop membrane fouling control technologies.

It is noteworthy that the recycling of hypersaline wastewater is highly impacted by its complex composition. Therefore, multi-process integrated approaches should be developed based on the actual water quality to accomplish the recycling of hypersaline wastewater in a green, low-carbon, and efficient manner.

(3)   Mechanism and critical path of synergies between atmospheric pollution control and carbon emission mitigation

Both atmospheric pollutant emissions and CO2 emissions show agglomeration effects in space, and the grids of hotspots are highly consistent. These hotspots are mainly distributed in large and medium-sized cities such as provincial capitals (capitals of autonomous regions) and key urban agglomerations. Similar to pollutant emissions, PM2.5 pollution and O3 pollution in China also show obvious regional characteristics, and the areas with heavy air pollution and CO2 emission areas are highly overlapped. The same root and homology of greenhouse gases and atmospheric pollutants makes the emission reduction work direction highly consistent, and the coordinated governance work can simultaneously achieve the dual goals of in-depth pollution prevention and control and “carbon peaking and carbon neutrality”, and promote the reduction of carbon emissions. Synergistic effect of pollution reduction and carbon reduction.

Considering that environmental pollutants and greenhouse gases have the same root and the same source, pollution reduction and carbon reduction are highly consistent in terms of management and control ideas, management methods, task measures, etc., and can be planned, integrated, and coordinated to achieve cost reduction and efficiency. Therefore, it is necessary to reveal the comprehensive impact mechanism of the application of pollution reduction and carbon reduction technology on social economy, ecosystem and human health through key research, as well as the feedback mechanism of cross-system element coupling and linkage on different technologies, and calculate the energy saving and emission reduction potential of the circular economy development model. Quantitative simulation and targeted regulation methods for the synergy of material energy flow and pollution reduction and carbon reduction in the coupled system of man and nature, develop a coupled multi-scale economy-energy-environment-climate model, and combine multi-source data from the Internet of Things and the Internet to reduce atmospheric pollution and carbon emissions Carry out accurate detection and evaluation, develop technologies and methods for collaborative governance of greenhouse gases and air pollutants, explore key paths for collaborative governance, and form a technical system and decision-making system support to achieve the goal of carbon neutrality.

(4)   Ecological effects and risks of microplastics in coastal wetlands or offshore waters

Microplastics are plastic particles, fibers, films or fragments less than 5 mm in diameter, which are difficult to degrade in the natural environment and can persist and migrate over long distances as microplastics are petroleum-based and carbon- chain polymers. Microplastics can alter the physicochemical properties of the abiotic environment and cause toxic damage to the growth traits and physiological and biochemical characteristics of plants, animals and microorganisms. Meanwhile, microplastics can release chemical additives such as Bisphenol A (BPA), phthalates and antioxidants during natural aging. In addition, microplastics are able to carry pathogenic microorganisms and other contaminants such as heavy metals, antibiotics and endocrine disruptors, and finally form complex contamination.

In recent years, there have been increasing studies on the environmental behavior and toxicological effects of microplastics in terrestrial and marine ecosystems. In contrast, few works have been conducted on microplastic pollution in coastal wetlands or offshore waters. Coastal wetlands and offshore waters play an important role in maintaining the balance between land and sea, protecting biodiversity, and improving the coastal environment. Seaward rivers have been identified as an important transport pathway for terrestrial plastic debris into the ocean. As a transition zone between terrestrial and marine ecosystems, coastal wetlands and offshore waters have become filters and sinks for microplastics. Offshore pollution from ship traffic, fisheries, oil well exploration, coastal agriculture and tourism is another important source of microplastics in the marine environment. At the same time, microplastics in the ocean can be transported back to coastal wetlands and offshore waters by wind-driven, ocean current circulation and tidal flows. Microplastic pollution in coastal wetlands and offshore waters is becoming more and more serious, but the ecological risks posed by microplastics to coastal wetlands or offshore waters are not yet clear. Therefore, the distribution characteristics and transport pathways of microplastics in coastal wetlands and offshore waters need to be further investigated, and the toxic mechanisms and ecological effects of microplastics on the ecosystem structure and function of coastal wetlands and offshore waters need to be further clarified.

(5)  Carbon sequestration of coastal wetland ecosystem

Out of all the biological carbon captured in Earth’s ecosystems, over half (55%) is captured by marine living organisms, which is called “blue carbon” (relative to the “green carbon” fixed by terrestrial ecosystems). The coastal wetland ecosystems mainly including mangroves, salt marsh wetlands and seagrass beds. The carbon captured by them is called coastal blue carbon. Compared with other ecosystems, the coastal wetland ecosystems have a very high carbon sequestration rate. In addition, the coastal wetland ecosystems are located between the sea and land, which are significantly affected by sea-land interactions. They are also eco-fragile regions and sensitive environmental areas that are greatly affected by human activities and climate change. Protecting and repairing the coastal wetland ecosystems and restoring the lost wetlands are contribute to carbon neutrality goals. Therefore, the study of carbon sequestration in coastal wetland ecosystems has received extensive attention in recent years.

At present, there have been many studies on blue carbon storage and carbon sequestration potential, but the carbon measurement methods used in different regions are not the same, which is not conducive to the comprehensive comparison and global analysis of coastal blue carbon. Besides, the carbon sink capacity of coastal wetland ecosystem is dynamic, and its carbon sequestration potential under the dual impact of climate change and human activities is also full of uncertainty. In response to these problems, the current main research directions and development trends include: first, it is necessary to study how to reduce the uncertainty in assessment of blue carbon in the coastal wetland ecosystems, deepen the understanding of carbon sequestration mechanism, and establish carbon sink measurement and assessment systems; second, it is necessary to analyze the impact of climate change and human activities on coastal wetland ecosystems and explain its evolution; third, it is necessary to study the technologies of carbon sequestration, assess the potential and stability of carbon sink enhancement in coastal wetland ecosystems, explore the protection, restoration and management methods for coastal wetland ecosystems based on natural solutions, and realize the synergistic improvement of the carbon sequestration and sink enhancement function of coastal wetland ecosystems and other important ecosystem functions; forth, it is necessary to select typical coastal wetlands, conduct evaluation and technology demonstration, and finally realize engineering and large-scale application.

(6)  Application of machine learning in earth system observation and prediction

Driven by an in-depth understanding of the mechanisms of the climate system, observational data, reanalysis data, and numerical simulations of the Earth system have grown rapidly over the past 40 years. In particular, a large number of climate models have participated in the fifth and the sixth phase of the International Coupled Model Intercomparison Project (CMIP5 and CMIP6), providing tens of billions of bytes of data resources for research on climate change, climate prediction and climate projection. How to extract useful information and acquire new knowledge from “big data” poses new challenges to traditional analysis methods, and brings new opportunities for machine learning and artificial intelligence. Machine learning can summarize key information and main features from the “big data” of the earth system, so as to make accurate identification and prediction. For example, the sea surface temperature information of a key area can improve the climate prediction skills of a certain area on the land in the coming months; on this basis, artificial intelligence can provide automated early warning of extreme weather and climate events. At present, machine learning, especially deep learning, has been widely studied in convective short-term nowcasting, extreme event detection and improvement of numerical weather models and their forecast error correction. The next step will be to change the traditional meteorological observation model, to accelerate and improve the processing of meteorological observation data, improve the quality of numerical weather forecasting, and advance the intersection of earth sciences.

(7) Vital characteristics and ecological effects of microorganisms in extreme marine environments

Extreme marine environments such as the deep sea, Polar Regions, submarine hydrothermal regions, and cold springs are characterized by harsh environmental conditions, including abnormal salinity, pressure, temperature, acidity, alkalinity, and radiation intensity. Nonetheless, a large number of extremophilic microorganisms survive these conditions. Investigating microorganisms that inhabit extreme marine environments, with their diversity, unique biological structures, and novel metabolic mechanisms, provides a valuable source of knowledge for exploring the origin, adaptation, and evolution of life. Moreover, marine extremophiles can produce novel active substances, including enzymes and other natural products, with broad potential uses. In addition, marine extremophiles are responsible for mineralizing and reusing organic matter in specific habitats as drivers of the transfer of nutrients, energy, and biogeochemical cycles.

At present, the primary research focuses are community structure and ecological functions of marine extremophiles, their symbiotic relationships with benthic organisms, their adaptation and evolutionary mechanisms for survival in extreme environments, the extraction of active substances from extremophiles, and their participation in biogeochemical cycling processes and environmental effect. In the future, it will be necessary to improve marine extremophile isolation and cultivation capabilities and to analyze their genetic structures and physiological metabolisms. It will also be essential to characterize the mode of action of their active products, explore their roles and interactions in the ecological processes of extreme environments, and elucidate their influence and regulatory functions on extreme environmental ecosystems.

(8)  Research on the cleaner production technology of tanning agent-free leather making

Chrome tanning technology based on the theory of “cross- linking tanning” occupies a dominant position in leather manufacturing, but the conventional chrome tanning technology suffers from the chrome emission issue. To address this problem, tanning chemists have developed chrome-free tanning agents represented by non-chrome metal tanning agents and organic tanning agents, which is aimed to replace conventional chrome tanning agents to form cross-linkages among collagen fibers to obtain tanning effects so as to fundamentally solve the problem of chrome emission. Nevertheless, the existing chrome-free tanned leathers fail to provide comparable thermal stability, mechanical strength and other leather properties to chrome-tanned leathers. In addition, the chrome-free tanning techniques still suffer from the emission problems of metals and organic pollutants. Aiming at the bottleneck of chrome-free tanning technologies based on the existing “cross-linking tanning” theory, it is of great significance to develop new tanning theories and tanning technologies to achieve cleaner production in the leather industry. During the conversion of raw hide into leather, its water content is significantly reduced, which also shows obviously improved fiber dispersion and porosity. Therefore, the tanning process can be regarded as a “controllable dehydration” process involved with reduced hydrophilicity and improved fiber dispersion. In these considerations, controllable removal of free water in raw hides with suitable dehydration media is expected to impart collagen fibers with high dispersibility and porosity, thereby significantly enhancing the thermal stability, mechanical strength and other leather properties without the usage of cross-linking agents. Hence, the pollutant emission problems in leather industry are able to be radically resolved, thus boosting the realization of cleaner production of tanning agent-free leather making. Polar organic solvents have the capabilities to provide efficient dehydration role, which are able to be applied in reducing the water content of raw hide effectively. However, the water distribution between organic solvent and raw hide will gradually reach a balance along with the dehydration to proceed, which requires multiple organic solvent changes to achieve deep dehydration performance, thus resulting some problems such as excessive consumption of organic solvents, complicated dehydration process and difficulty in recycling of waste solvents. To this end, the composite dehydration media composed of porous materials and polar organic solvents was developed for realizing the one-step controllable deep dehydration. The porous materials are capable of selectively adsorbing and storing the captured water in the organic solvents, thereby breaking the distribution balance of water between the organic solvent and raw hide. Moreover, the used composite dehydration media were facilely recycled through the solid-liquid separation and reused for tanning agent-free leather making after regeneration. In the future, it is essential to further develop novel composite dehydration media to strengthen the controllable deep dehydration performance of raw hides and consummate the technical routes of tanning agent-free leather making, which in turn lays the foundation for the industrial application of cleaner production technology of tanning agent-free leather making so as to promote the sustainable and green development of the leather industry.

(9)  Study on the mechanisms of food functional factors and chronic metabolic syndrome

Food functional factors such as polysaccharides, polyphenols and flavonoids in animals, plants and fungi have many excellent biological activities such as preventing obesity and diabetes, regulating glucolipid metabolism, and improving obesity induction, which have positive effects on improving human health. Therefore, it is important to study the mechanism of food functional factors in the prevention of chronic metabolic syndrome at molecular, cellular and overall levels to provide theoretical and technical support for the early prevention and nutritional intervention of nutrition- related chronic diseases. Meanwhile, the enrichment of food functional factors and their bioactive system evaluation will be studied and functional foods with applications for the prevention of metabolic syndrome will be developed. Rapid and efficient screening and identification of natural functional components (such as terpenoids, flavonoids, phenols, alkaloids, saponins, etc.) in new food ingredients that act on obesity, diabetes, immunity, hypertension, lipid dysfunction and cancer through modern molecular biology, cell biology, metabolomics, molecular nutrition and other biological, chemical, physical and chemical technologies.

(10) Extraction and development of new natural cellulose fibers

Since petrochemical resources are becoming more scarce and environmental problems are becoming increasingly significant, natural cellulose fibers have gained increasing attention for their green, clean, and environmentally friendly characteristics, unique properties, renewable raw materials, natural degradation after disposal, and non-toxic and harmless properties. Natural cellulose fiber is a type of natural fiber containing cellulose as the main component. Since it is derived from plants, it is also referred to as plant fiber. The natural cellulose fiber is environmentally friendly. It is of great significance to the sustainable use of natural resources and the protection of the environment to conduct research and development of new natural cellulose fibers.

There are currently several research difficulties associated with the cellulose science field: one is the extraction of natural cellulose fibers; the second is the research of cellulose dissolving systems; and the third is the development of new functional natural cellulose fibers. It is particularly important to know how to cleanly and efficiently separate cellulose from plant cell walls (natural fibers). Plants have a very complex cell wall structure. The outer layer is protected by wax and inorganic salts. Chemical components such as hemicellulose and lignin are closely related to the inner cellulose. All of these factors pose obstacles to the separation and extraction of cellulose. There are two types of separation and extraction techniques that are commonly used today: biological and chemical. After biological extraction, cellulose contains a significant amount of gum, and the activity of biological enzymes is poor. The chemical method is the most widely used, but it also involves a complex process and consumes a great deal of energy. To further realize the development of high value-added functional natural cellulose fiber textiles, it is necessary to pursue the green and efficient separation, extraction, and research and development of new natural cellulose fibers.

《1.2 Interpretations for three key engineering research fronts》

1.2 Interpretations for three key engineering research fronts

1.2.1 Mechanisms of multi-media transport and transfor- mation of new pollutants

New pollutants (or emerging pollutants) refer to newly discovered or noticed pollutants that pose risks to the ecological environment or human health, and have not yet been incorporated into management or existing management measures are insufficient to effectively prevent and control their risks. With the increasing understanding of the environmental and health hazards of chemical substances and the continuous development of environmental monitoring technology, the number of new pollutants that can be identified will continue to increase. Therefore, the development of efficient and universal analytical methods for discovering new pollutants is an important research direction in the field of new pollutant management. Figure 1.2.1 is the roadmap of the engineering research front of “mechanisms of multi-media transport and transformation of new pollutants”.

The production and use of toxic and hazardous chemical substances are the main sources of new pollutants. Literature shows that higher levels of new pollutants such as environmental endocrine disruptors, antibiotics, and microplastics have been monitored successively in the atmosphere, water, and soil in some regions of China. Transfer of new pollutants among different environmental media often occurs, implying that one medium can become the pollution source for the next environmental medium, leading to differences in fate and contamination levels for new pollutants in different media. However, the migration and transformation behaviors and mechanisms of most new pollutants among multi-media are unclear, and the health risks are unclear. Around the management of new pollutants, it is necessary to further strengthen the research on environmental screening, traceability studies, environmental risk assessment and control, and research on ecological and environmental hazard mechanisms such as antibiotics and microplastics; it is also a necessary to develop with the help of mathematical methods or models to better describe the cross-media migration and transformation of new pollutants released into the atmosphere.

Table 1.2.1 shows countries with the largest output of core papers on “mechanisms of multi-media transport and transformation of new pollutants”. Among them, China ranked first with 42.74% of core papers and 3 637 citations. There is a large gap between other countries and China, which indicates that China has strong research advantages in this field. In terms of citations per paper, although the number of core papers in Spain is small, its citations per paper rank first, which also shows the importance of publishing high-level core papers recognized by peers from one side.

Table 1.2.2 shows the main output institutions of core papers in this engineering research frontier. Six of the top ten output institutions are from Chinese research institutions, namely, Chinese Academy of Sciences, East China Normal University,

《Figure 1.2.1》

Figure 1.2.1 Roadmap of the engineering research front of “mechanisms of multi-media transport and transformation of new pollutants”

《Table 1.2.1》

Table 1.2.1 Countries with the greatest output of core papers on “mechanisms of multi-media transport and transformation of new pollutants”

Tsinghua University, Guangdong University of Technology, Northwest A&F University, and Nankai University. Among them, Chinese Academy of Sciences ranked first in the number of institutions with 20 core papers.

As can be seen from Figure 1.2.2, more emphasis is placed on inter-country cooperation in this research area by China, the USA, India, and the UK. China has the highest number of published papers, mainly with India, the UK, and Germany for collaborative publication. According to Figure 1.2.3, Chinese Academy of Sciences, Norwegian Institute of Air Research, Nankai University, and East China Normal University have cooperative relations.

Based on Table 1.2.3, the country with the highest output of citing core papers is China, with 46.41% of citing core papers, followed by the USA with 12.31%. As presented in Table 1.2.4, the institution with the highest output of citing core papers is Chinese Academy of Sciences, with 36.12% of citing core papers, followed by Hunan University, with 12.15% of citing core papers.

The results of the above data analysis show that China is the forefront of the world in the output and the number of citing core papers on the mechanism of multi-media transport and transformation of new pollutants, followed by the USA.

1.2.2 Carbon sequestration of coastal wetland ecosystem

The carbon fixed by the coastal wetland ecosystems such

《Table 1.2.2》

Table 1.2.2 Institutions with the greatest output of core papers on “mechanisms of multi-media transport and transformation of new pollutants”

《Figure 1.2.2》

Figure 1.2.2 Collaboration network among major countries in the engineering research front of “mechanisms of multi-media transport and transformation of new pollutants”

《Figure 1.2.3》

Figure 1.2.3 Collaboration network among major institutions in the engineering research front of “mechanisms of multi-media transport and transformation of new pollutants”

《Table 1.2.3》

Table 1.2.3 Countries with the greatest output of citing papers on “mechanisms of multi-media transport and transformation of new pollutants”

《Table 1.2.4》

Table 1.2.4 Institutions with the greatest output of citing papers on “mechanisms of multi-media transport and transformation of new pollutants”

as mangrove, salt marsh wetland and seagrass bed are the coastal blue carbon. The term “blue carbon” was first coined in 2009. Compared with the “green carbon” fixed by terrestrial ecosystems, it emphasizes the important contribution of ocean to carbon sequestration. The carbon sequestration of coastal wetland ecosystems is mainly reflected in plant carbon sequestration and sediment carbon burial in the vertical direction, and carbon exchange with seawater in the horizontal direction. The reciprocating tidal can slow down the decomposition of organic matter, continuously accumulate of the sediments and create an anaerobic environment in the coastal wetlands. The decomposition of organic matter is inhibited, and the carbon in the sediments can be kept in a stable state for a long time under certain conditions and realize continuous carbon storage. Compared with other ecosystems, the coastal wetland ecosystems have a very high carbon sequestration rate. In addition, the coastal wetlands also provide ecosystem service functions such as storm protection, wave dissipation, climate regulation, water purification, spiritual and aesthetic, and nutrient cycling, which has significant social and economic benefits.

The protection and restoration of the coastal ecosystems under human intervention is an operable way to increase carbon sinks. The existing technologies for coastal wetland restoration to increase carbon sinks include rebuilding high biomass plant communities, amending the sediment, conservating the beach, improving the wetland soil and the water environment. At present, the “nature-based solutions” are mainly advocated to realize the synergistic improvement of the carbon sequestration and sink enhancement of coastal wetland ecosystems and other important ecosystem functions. Figure 1.2.4 is the roadmap of the engineering research front of “carbon sequestration of coastal wetland ecosystem”.

The main research directions and development trends at present include: ① analyzing the carbon source and carbon fixation mechanism, establishing the monitoring network, the big data platform, and carbon assessment systems, achieving long-term real-time monitoring; ② based on the spatial- temporal pattern of blue carbon, exploring the key regulatory factors of climate change and human activities that affect the blue carbon, deepening the understanding of carbon sequestration mechanism and evolution, and assessing the potential and sustainability of coastal wetland ecosystems in increasing carbon sinks; ③ studying the technologies of carbon sequestration, assessing the potential and stability of carbon sink enhancement in coastal wetland ecosystems, establishing the frameworks for coastal wetlands protection, restoration and management based on natural solutions, studying the service value evaluation methods of the coastal wetland ecosystems, exploring how to protect the integrity of coastal wetland ecosystems functions, and realizing the coordinated improvement of carbon sequestration and sink enhancement and other ecosystem functions; ④ selecting typical coastal wetlands, conduct evaluation and technology demonstration, and realizing the engineering and large-scale application of technologies for synergistic improvement of various ecosystem functions.

《Figure 1.2.4》

Figure 1.2.4 Roadamp of the engineering research front of “carbon sequestration of coastal wetland ecosystem”

Among the countries with the greatest output of core papers on this research (Table 1.2.5), the number of core papers and citation frequency of the USA are the first, and the number of core papers of China is the second. The total number of core papers of China and the USA accounts for more than half of the total number of the top 10 countries. In terms of the collaboration network among major countries on this research (Figure 1.2.5), the cooperation among the top 10 countries is close. In terms of institutions with the greatest output of core papers on this research (Table 1.2.6), the top 10 institutions with core papers are concentrated in China and the USA. In the collaboration network among major institutions (Figure 1.2.6), there is close cooperation among various institutions. In the ranking of countries with the greatest output of citing papers (Table 1.2.7), China ranks first, while the Chinese Acad Sci, Beijing Normal Univ and East China Normal Univ rank first, second and fifth respectively in the ranking of institutions with the greatest output of citing papers (Table 1.2.8). In short, although the USA is still in the leading position in the world, China has also accelerated the pace of catching up. China still needs to accelerate its development, narrow the gap with the USA, and improve the international influence and discourse power of research in this field.

《Table 1.2.5》

Table 1.2.5 Countries with the greatest output of core papers on “carbon sequestration of coastal wetland ecosystem”

《Figure 1.2.5》

Figure 1.2.5 Collaboration network among major countries in the engineering research front of “carbon sequestration of coastal wetland ecosystem”

《Table 1.2.6》

Table 1.2.6 Institutions with the greatest output of core papers on “carbon sequestration of coastal wetland ecosystem”

《Figure 1.2.6》

Figure 1.2.6 Collaboration network among major institutions in the engineering research front of “carbon sequestration of coastal wetland ecosystem”

《Table 1.2.7》

Table 1.2.7 Countries with the greatest output of citing papers on “carbon sequestration of coastal wetland ecosystem”

《Table 1.2.8》

Table 1.2.8 Institutions with the greatest output of citing papers on “carbon sequestration of coastal wetland ecosystem”

1.2.3 Research on the cleaner production technology of tanning agent-free leather making

Tanning refers to the qualitative transformation process of converting raw hide into leather, which is one of the most important sections in the leather manufacturing. Chrome tanning technology based on the usage of chrome salts as tanning agents occupies a dominant position in leather manufacturing for a long time due to its excellent cross-linking tanning effect. However, chrome emission is a persisting problem in chrome tanning process, which is suffered by the limited absorption capability of raw hide to chrome tanning agent. To address this issue, great efforts have been dedicated to developing chrome-free tanning techniques based on the “cross-linking tanning” theory, which is aimed to replace conventional chrome tanning agents to form cross- linkages among collagen fibers to obtain tanning effects so as to fundamentally solve the problem of chrome emission. At present, the already reported chrome-free tanning agents mainly include non-chrome metal tanning agents and organic tanning agents, while these chrome-free tanned leathers fail to provide comparable thermal stability, mechanical strength and other leather properties to chrome-tanned leathers. In addition, the chrome-free tanning techniques still suffer from the emission problems of metals and organic pollutants. Figure 1.2.7 is the roadmap of the engineering research front of “research on the cleaner production technology of tanning agent-free leather making”.

Aiming at the bottleneck of chrome-free tanning technologies based on the existing “cross-linking tanning” theory, it is of great significance to develop new tanning theories and tanning technologies to achieve cleaner production in the leather industry. Extensive tanning practices indicate that the tanned leather has lower water content as compared with raw hide, which also shows obviously improved fiber dispersion and porosity. Therefore, the tanning process can be regarded as a “controllable dehydration” process involved with reduced hydrophilicity and improved fiber dispersion. In these considerations, controllable removal of free water in raw hides with suitable dehydration media is expected to impart collagen fibers with high dispersibility and porosity, thereby significantly enhancing the thermal stability, mechanical strength and other leather properties without the usage of cross-linking agents. Hence, the pollutant emission problems in leather industry are able to be radically resolved, thus boosting the realization of cleaner production of tanning agent-free leather making.

《Figure 1.2.7》

Figure 1.2.7 Roadmap of the engineering research front of “research on the cleaner production technology of tanning agent-free leather making”

Polar organic solvents have the capabilities to provide efficient dehydration role, which are able to be applied in reducing the water content of raw hide effectively. However, the water distribution between organic solvent and raw hide will gradually reach a balance along with the dehydration to proceed, which requires multiple organic solvent changes to achieve deep dehydration performance, thus resulting some problems such as excessive consumption of organic solvents, complicated dehydration process and difficulty in recycling of waste solvents. To this end, the composite dehydration media composed of porous materials and polar organic solvents was developed for realizing the one-step controllable deep dehydration. The porous materials are capable of selectively adsorbing and storing the captured water in the organic solvents, thereby breaking the distribution balance of water between the organic solvent and raw hide so as to keep a constant low water content during the whole dehydration process for realizing continuous dehydration of raw hide. Moreover, the used composite dehydration media were facilely recycled through the solid-liquid separation and reused for tanning agent-free leather making after regeneration. In the future, it is essential to further develop novel composite dehydration media to strengthen the controllable deep dehydration performance of raw hides and consummate the technical routes of tanning agent-free leather making, which in turn lays the foundation for the industrial application of cleaner production technology of tanning agent-free leather making so as to promote the sustainable and green development of the leather industry.

Through the interpretations of core papers on “research on the cleaner production technology of tanning agent-free leather making”, it was found that the citation per paper was relatively low as 5.42 times since this engineering front is still in the early research stage (Table 1.1.1). Table 1.2.9 shows the countries with the greatest output of core papers on this research fronts. Among them, China ranks first with a core paper percentage of 70.83% and a citation of 114 times, which indicates that many Chinese experts and scholars are committed to this front of research. In addition, China also leads other countries and regions in the citations per paper. India ranks second in the two indicators of core paper ratio and citations per paper. In terms of the major output countries or regional cooperation networks (Figure 1.2.8), China and Brazil displayed strong independent research and development capabilities in this field, and many countries also have cooperated extensively.

As shown in Table 1.2.10, the top eight output institutions are all from China, which further indicates that Chinese researchers are highly enthusiastic about this research front. Among them, the top institutions in terms of the percentage of core paper and citation per paper are all Sichuan University, reflecting the leading role of this institution in the engineering front of “research on the cleaner production technology of tanning agent-free leather making”. According to the main inter-agency cooperation network (Figure 1.2.9), most of the institutions have worked in cooperation with other institutions, and a small number of institutions mainly rely on the independent research and development.

As for the ranking of citing papers of this research front, China still occupies a leading position in the world with 54.17% (Table 1.2.11). In addition, the number of citing core papers of Sichuan University and Shaanxi University of Science and Technology leads other scientific research institutions (Table 1.2.12).

Overall, China is not only ahead of other countries in the world, but also has strong independent research and development capabilities in the engineering research front on “research on the cleaner production technology of

《Table 1.2.9》

Table 1.2.9 Countries with the greatest output of core papers on “research on the cleaner production technology of tanning agent-free leather making”

《Figure 1.2.8》

Figure 1.2.8 Collaboration network among major countries or regions in the engineering research front of “research on the cleaner production technology of tanning agent-free leather making”

《Table 1.2.10》

Table 1.2.10 Institutions with the greatest output of core papers on “research on the cleaner production technology of tanning agent-free leather making”

《Figure 1.2.9》

Figure 1.2.9 Collaboration network among major institutions in the engineering research front of “research on the cleaner production technology of tanning agent-free leather making”

《Table 1.2.11》

Table 1.2.11 Countries with the greatest output of citing papers on “research on the cleaner production technology of tanning agent-free leather making”

《Table 1.2.12》

Table 1.2.12 Institutions with the greatest output of citing papers on “research on the cleaner production technology of tanning agent-free leather making”

tanning agent-free leather making”. It is recommended that the research institutions should continue to carry out in- depth research in related fields so as to maintain the research status of this research front, and promote the technological development of related industries around the world.

《2 Engineering development fronts》

2 Engineering development fronts

《2.1 Trends in Top 10 engineering development fronts》

2.1 Trends in Top 10 engineering development fronts

The Top 10 engineering development fronts in the field of environmental and light textile engineering are summarized in Table 2.1.1. These include the subfields of environmental science, meteorological science, marine science, food science, textile science, and light industry science. The number of patents related to these individual topics between 2016 and 2021 is presented in Table 2.1.2.

(1)  Collaborative control technology of high-quality recycling of solid waste and pollution and carbon reduction

The collaborative control technology of high-quality recycling of solid waste and pollution and carbon reduction is the key to realize green recycling and low-carbon development. There is an urgent need to: develop green alternative materials, improve the production process, and reduce the output of solid waste sources; research and develop multi-dimensional green, low-carbon and high-value utilization technologies for solid waste in key industries, taking into account the risk prevention and control of carbon emission reduction and

《Table 2.1.1》

Table 2.1.1 Top 10 engineering development fronts in environmental and light textile engineering

《Table 2.1.2》

Table 2.1.2 Annual number of core patents published for the Top 10 engineering development fronts in environmental and light textile engineering