Experimental and Theoretical Study on Carbonization Coefficient Model of NS/SAP Concrete

Carbonization coefficient research has great significance in concrete carbonization evaluation. Nano-silica (NS) can reduce the content of Ca(OH)2, which is generated during the hydration of concrete, resulting in improved carbonization resistance and compressive strength of concrete. This paper investigates the carbonization effects of concrete with internal curing, such as Super Absorbent Polymer (SAP). The research shows that SAP can promote hydration of the internal concrete but form tiny pores after releasing the water completely, which may cause a reduction of carbonation resistance of concrete. The concrete was modified by adding SAP, ranging from 0 to 0.24%, to ascertain the optimal content of SAP. The addition of NS changed the concrete from 0 to 1.5% to confirm the optimal range of NS. To establish a reasonable suitable theoretical model of NS/SAP concrete, the influence factors of the carbonization coefficient of concrete were analyzed first. Later, the accelerated carbonization test was carried out on 100 mm × 100 mm × 100 mm cube specimens with different carbonization time to obtain the compressive strength and carbonization depth to establish the carbonization coefficient model of NS/SAP concrete. Before analyzing experimental data, the specimens were randomly divided into fitting and validation groups. Based on the regression analysis of the fitting group, the carbonization coefficient model was established, which embodied the influence of various parameters on concrete carbonization, including SAP content, NS content, water–cement ratio, CO2 concentration, temperature, relative humidity, and compressive strength. According to the validation analysis of the verification group, the mean relative error of the model is 5.04%, and the residual mean square error is 0.1751. Compared with the literature models, this study’s carbonization model can accurately predict the carbonization depth of NS/SAP concrete

Experimental and Theoretical Study on Carbonization Coefficient Model of NS/SAP Concrete

Carbonization coefficient research has great significance in concrete carbonization evaluation. Nano-silica (NS) can reduce the content of Ca(OH)2, which is generated during the hydration of concrete, resulting in improved carbonization resistance and compressive strength of concrete. This paper investigates the carbonization effects of concrete with internal curing, such as Super Absorbent Polymer (SAP). The research shows that SAP can promote hydration of the internal concrete but form tiny pores after releasing the water completely, which may cause a reduction of carbonation resistance of concrete. The concrete was modified by adding SAP, ranging from 0 to 0.24%, to ascertain the optimal content of SAP. The addition of NS changed the concrete from 0 to 1.5% to confirm the optimal range of NS. To establish a reasonable suitable theoretical model of NS/SAP concrete, the influence factors of the carbonization coefficient of concrete were analyzed first. Later, the accelerated carbonization test was carried out on 100 mm × 100 mm × 100 mm cube specimens with different carbonization time to obtain the compressive strength and carbonization depth to establish the carbonization coefficient model of NS/SAP concrete. Before analyzing experimental data, the specimens were randomly divided into fitting and validation groups. Based on the regression analysis of the fitting group, the carbonization coefficient model was established, which embodied the influence of various parameters on concrete carbonization, including SAP content, NS content, water–cement ratio, CO2 concentration, temperature, relative humidity, and compressive strength. According to the validation analysis of the verification group, the mean relative error of the model is 5.04%, and the residual mean square error is 0.1751. Compared with the literature models, this study’s carbonization model can accurately predict the carbonization depth of NS/SAP concrete

Rice Husk and Its Biochar Have Contrasting Effects on Water-Soluble Organic Matter and the Microbial Community in a Bamboo Forest Soil

Converting rice husk to biochar is one of the solutions to manage crop residues by transforming waste into a value-added material that has broad benefits to the environment when biochar is applied to the soil. This study investigated the impact of the application of rice husk and its biochar at different doses (i.e., 0, 10, and 30 t ha−1) on soil carbon stability, the property of water-soluble soil organic matter, and the abundance and diversity of microbial communities in a Lei bamboo (Phyllostachys praecox) forest soil 262 days after their application. The application of rice husk, especially at 30 t ha−1, increased dissolved organic carbon due to the high labile carbon (C) (e.g., cellulose, hemicellulose, polysaccharides) content in the rice husk. The biochar treatments stimulated the release of humic-like substances (e.g., (poly) phenols) into the soil solution, increased the aromatic C content by 412–557%, and increased the relative abundance of Chloroflexi, Planctomycetota, and Proteobacteria compared to the control. This study shows that biochar application, particularly at 30 t ha−1, enhanced the C stability by turning organic C into recalcitrant forms in the soil, demonstrating the merit of converting rice husk into biochar before its application to the soil

Increase in Cd Tolerance through Seed-Borne Endophytic Fungus Epichloë gansuensis Affected Root Exudates and Rhizosphere Bacterial Community of Achnatherum inebrians

Soil cadmium (Cd) pollution is a serious environmental problem imperiling food safety and human health. The endophyte Epichloë gansuensis can improve the tolerance of Achnatherum inebrians to Cd stress. However, it is still unknown whether and how the endophyte helps host plants build up a specific bacterial community when challenged by CdCl2. In this study, the responses of the structure and function of bacterial community and root exudates of E+ (E. gansuensis infected) and E− (E. gansuensis uninfected) plants to Cd stress were investigated. Analysis of bacterial community structure indicated that the rhizosphere bacterial community predominated over the root endosphere bacterial community in enhancing the resistance of CdCl2 in a host mediated by E. gansuensis. E+ plant strengthened the interspecific cooperation of rhizosphere bacterial species. Moreover, the analysis of root exudates demonstrated E. gansuensis and increased the contents of organic acids and amino acids under Cd stress, and most root exudates were significantly correlated with rhizosphere bacteria. These results suggested that E. gansuensis employed a specific strategy to recruit distinct rhizosphere bacterial species and relevant functions by affecting root exudates to improve the tolerance of the host to Cd stress. This study provides a firm foundation for the potential application of symbionts in improving phytostabilization efficiency

Trophic transfer of silver nanoparticles shifts metabolism in snails and reduces food safety.

Food security and sustainable development of agriculture has been a key challenge for decades. To support this, nanotechnology in the agricultural sectors increases productivity and food security, while leaving complex environmental negative impacts including pollution of the human food chains by nanoparticles. Here we model the effects of silver nanoparticles (Ag-NPs) in a food chain consisting of soil-grown lettuce Lactuca sativa and snail Achatina fulica. Soil-grown lettuce were exposed to sulfurized Ag-NPs via root or metallic Ag-NPs via leaves before fed to snails. We discover an important biomagnification of silver in snails sourced from plant root uptake, with trophic transfer factors of 2.0–5.9 in soft tissues. NPs shifts from original size (55–68 nm) toward much smaller size (17–26 nm) in snails. Trophic transfer of Ag-NPs reprograms the global metabolic profile by down-regulating or up-regulating metabolites for up to 0.25- or 4.20- fold, respectively, relative to the control. These metabolites control osmoregulation, phospholipid, energy, and amino acid metabolism in snails, reflecting molecular pathways of biomagnification and pontential adverse biological effects on lower trophic levels. Consumption of these Ag-NP contaminated snails causes non-carcinogenic effects on human health. Global public health risks decrease by 72% under foliar Ag-NP application in agriculture or through a reduction in the consumption of snails sourced from root application. The latter strategy is at the expense of domestic economic losses in food security of $177.3 and$58.3 million annually for countries such as Nigeria and Cameroon. Foliar Ag-NP application in nano-agriculture has lower hazard quotient risks on public health than root application to ensure global food safety, as brought forward by the United Nations Sustainable Development Goals.Environmental Biolog

TX Microelectrode Studies on the Pitting Corrosion Process of Stainless Steel

应用微电极法研究不锈钢点腐蚀发生发展过程，首次获得不锈钢夹杂物缺陷在阳极活化电位的活性溶解信息和点腐蚀发展过程蚀点生长和消止两个相互竞争、不断发展的动态行为，深化对夹杂物缺陷诱导点腐蚀的发生及点腐蚀发展过程机理的认识。实验表明，应用微电极技术研究点腐蚀过程可具有若干明显特点：ａ．由于界面双层电容和背景电流的大幅度降低，有利于检测点腐蚀发生和发展过程快速、信号微弱；ｂ．可考察夹杂物缺陷的电化学活性及其诱导点腐蚀成核的重要作用；ｃ．可研究单孔点腐蚀发展的动态行为及影响因素。Abstract Differing with the scanning microelectrode techniques, which scan microelctrode closely to the interface of electrode/electrolyte and make electrochemical imaging in a lateral spatial resolution, the technique of microelectrode with a micron diameter is of very high timeresolution and ratio of signal/noise in electrochemical measurements. The microelectrode technique allows doublelayer capacitance and background current for a microelectrode to be drastically reduced due to the exposed area of a microelectrode is usually 6～8 orders of magnetite lower than that of a conventional electrode with largescale exposed area. Microelectrode was recently developed as a new powerful electrochemical technique and widely used in the studies of electrochemical kinetics, electrodeposition, electroanalysis and batteries. However, most of the microelectrodes was limited with the novel metals, such as Pt and Au, and only a little of work has reported on using microelectrode in corrosion research. In the present work, the microelectrode technique was developed to study the initiation and propagation of pitting corrosion of 18/8 stainless steel. The insight into the dissolution process of inclusion defects at the anodic potential of active dissolution and the dynamic behavior of growth and ceases for the micropitting during its development was attained. Microelectrode technique may offer a numbers of advantages for further recognizing the mechanism of pitting corrosion: to catch the fast and weak signal in an early stage of pitting initiation because of extreme low in both of doublelayer capacitance and background current for a microelectrode; to clarify the dependence of pitting nucleation on the inhomogenious defects; and to follow the propagation process for a simulated single pitting corrosion.作者联系地址：厦门大学固体表面物理化学国家重点实验室Author's Address: State Key Lab for Phys. Chem. of Solid Surfs., Dept. of Mat. Sci., Dept. of Chem., Inst. of Phys. Chem., Xiamen University, Xiamen 36100