Research and development on mechanism of removal of indoor volatile organic compounds by plants

Background,aim,and scope Owing to the rapid development of modernisation and urbanisation,living standards have gradually improved.However,the widespread use of high-energy-consuming indoor appliances and furniture has made indoor environments a primary environmental problem affecting human health.Sick building syndrome(SBS)and building-related illness(BRI)have occurred,and indoor air conditions have been extensively studied.Common indoor pollutants include CO,CO_(2),volatile organic compounds(VOCs)(such as the formaldehyde and benzene series),NOx(NO and NO_(2)),and polycyclic aromatic hydrocarbons(PAHs).VOCs have replaced SO_(2)as the“The Fourteenth Five-Year Plan”urban air quality assessment new indicators.Indoor VOCs can cause diseases such as cataract,asthma,and lung cancer.To protect human health,researchers have proposed several indoor air purification technologies,including adsorption,filtration,electrostatic dust removal,ozonation,and plant purification.However,each technology has drawbacks,such as high operating costs,high energy consumption,and the generation of secondary waste or toxic substances.Plant degradation of VOCs as a bioremediation technology has the characteristics of low cost,high efficiency,and sustainability,thereby becoming a potential green solution for improving indoor air quality.This study introduces the research status and mechanism of plant removal of indoor VOCs and provides an experimental basis and scientific guidance for analysing the mechanism of plant degradation of pollutants.Materials and methods This study reviews studies on the harm caused by indoor pollutants to human health and related sources,mainly investigating the degradation of indoor formaldehyde,BTEX(benzene,toluene,ethylbenzene,and xylene)plant mechanisms,and research results.Results Plants can remove VOCs via stomatal and non-stomatal adsorption,interfoliar microbial,rhizosphere microbial,and growth media.Benzene,toluene,and xylene(BTX)are adsorbed by pores,hydroxylated into fumaric acid,and then removed into CO_(2) and H_(2)O by TCA.Formaldehyde enters plant leaves through the stomata and epidermal waxy substances and is adsorbed.After the two steps of enzymatic oxidation,formic acid and CO_(2) are generated.Finally,it enters the Calvin cycle and removes glucose and other nontoxic compounds.Discussion The non-stomatal degradation of VOCs can be divided into adsorption by cuticular wax and active adsorption by plant surface microorganisms.The leaf epidermal waxy matter content and the lipid composition of the epidermal membrane covering the plant surface play important roles in the non-stomatal adsorption of indoor air pollutants.The leaf margin of a plant is an ecological environment containing various microbial communities.The endophytic and inoculated microbiota in plant buds and leaves can remove VOCs(formaldehyde and BTEX).Formaldehyde can be directly absorbed by plant leaves and converted into organic acids,sugars,CO_(2) and H_(2)O by microbes.Bioremediation of indoor VOCs is usually inefficient,leading to plant toxicity or residual chemical substance volatilisation through leaves,followed by secondary pollution.Therefore,plants must be inoculated with microorganisms to improve the efficiency of plant degradation of VOCs.However,the effectiveness of interfoliar microbial removal remains largely unknown and several microorganisms are not culturable.Therefore,methods for collecting,identifying,and culturing microorganisms must be developed.As the leaf space is a relatively unstable environment,the degradation of VOCs by rhizosphere microorganisms is equally important,and formaldehyde is absorbed more by rhizosphere microorganisms at night.The inoculation of bacteria into the rhizosphere improves the efficiency of plants in degrading VOCs.However,most of these studies were conducted in simulation chambers.To ensure the authenticity of these conclusions,the ability of plants to remove indoor air pollutants must be further verified in real situations.Conclusions Plant purification is an economical,environment-friendly,and sustainable remediation technology.This review summarises the mechanisms of VOC plant degradation and presents its limitations.Simultaneously,it briefly puts forward a plant selection scheme according to different temperatures,light,and specific VOCs that can be absorbed to choose the appropriate plant species.However,some studies have denied the purification effect of plants and proposed that numerous plants are required to achieve indoor ventilation effects.Therefore,determining the ability of plants to remove indoor VOCs requires a combination of realistic and simulated scenarios.Recommendations and perspectives Plants and related microorganisms play an important role in improving indoor air quality,therefore,the effect of plants and the related microorganisms on improving indoor air quality must be studied further and the effect of plants on indoor VOCs will be the focus of future research.

Removal mechanisms of heavy metal pollution from urban runoff in wetlands

Solid particles, particularly urban surface dust in urban environments contain large quantities of pollu- tants. It is considered that urban surface dust is a major pollution source of urban stormwater runoff. The storm- water runoffwashes away urban surface dust and dissolves pollutants adsorbed onto the dust and finally discharges into receiving water bodies. The quality of receiving water bodies can be deteriorated by the dust and pollutants in it. Polluted waters can be purified by wetlands with various physical, chemical, and biologic processes. These pro- cesses have been employed to treat pollutants in urban stormwater runoff for many years because purification of treatment wetlands is a natural process and a low-cost method. In this paper, we reviewed the processes involved during pollutants transport in urban environments. Parti- cularly, when the urban stormwater runoff enters into wetlands, their removal mechanisms involving various physical, chemical and biologic processes should been understood. Wetlands can remove heavy metals by absorbing and binding them and make them form a part of sediment. However, heavy metals can be released into water when the conditions changed. This information is important for the use of wetlands for removing of pollutants and reusing stormwater.

Material removal mechanisms and characteristics of potassium dihydrogen phosphate crystals under nanoscratching

Potassium dihydrogen phosphate(KDP)crystals are important materials in high-energy laser systems.However,because these crystals are brittle and soft,machining-induced defects often emerge in KDP components.This study aimed to investigate the material removal mechanisms and characteristics of KDP during nanoscratching using Berkovich,spherical,and conical indenters.We found that KDP surface layers could be removed in a ductile mode at the micro/nanoscale and that dislocation motion was one of the main removal mechanisms.Removal characteristics are related to the stress fields generated by indenter geometries.The spherical indenter achieved a ductile removal mode more easily.The lateral force of nanoscratching increased with an increase in the normal force.The coefficient of friction(COF)followed the same trend as the lateral force when spherical and conical indenters were used.However,the COF was independent of the normal force when using a Berkovich indenter.We found that these COF variations could be accurately described by friction models.

Surfactant-Modified Hydrophobic Biochar Derived from Laver (Porphyra haitanensis) with Superior Removal Performance for Kitchen Oil

In this study,a novel absorpent(MSAR600℃)with a hydrophobic surface and hierarchical porous structure for the removal of kitchen oil was facilely fabricated from the macroalgae,laver(Porphyra haitanensis)by incorpor-ating high-temperature carbonization and alkyl polyglucosides(APG)and rhamnolipid(RL)surfactants modifi-cation.The characterization results showed MSAR600℃ possessed a louts-leaf-like papillae microstructure with high contact angle(137.5°),abundant porous structure with high specific surface area(23.4 m^(2)/g),and various oxygen-containing functional groups(-OH,C=O,C-O).Batch adsorption experiments were conducted to inves-tigate the effect of adsorption time,temperature,pH,and absorbent dose on kitchen oil adsorption performance.Then the practical application for the removal of kitchen oil using MSAR600℃ was also performed.The results showed that MSAR600℃ had a higher removal efficiency for kitchen oil(75.98%),compared with the commercial detergent(72.3%).This study demonstrates an example of fabricating a green tableware detergent for enhanced removal performance of kitchen oil.

Energy beam-based direct and assisted polishing techniques for diamond:A review

Diamond is a highly valuable material with diverse industrial applications,particularly in the fields of semiconductor,optics,and high-power electronics.However,its high hardness and chemical stability make it difficult to realize high-efficiency and ultra-low damage machining of diamond.To address these challenges,several polishing methods have been developed for both single crystal diamond(SCD)and polycrystalline diamond(PCD),including mechanical,chemical,laser,and ion beam processing methods.In this review,the characteristics and application scope of various polishing technologies for SCD and PCD are highlighted.Specifically,various energy beam-based direct and assisted polishing technologies,such as laser polishing,ion beam polishing,plasma-assisted polishing,and laser-assisted polishing,are summarized.The current research progress,material removal mechanism,and infuencing factors of each polishing technology are analyzed.Although some of these methods can achieve high material removal rates or reduce surface roughness,no single method can meet all the requirements.Finally,the future development prospects and application directions of different polishing technologies are presented.

Field-assisted machining of difficult-to-machine materials

Difficult-to-machine materials (DMMs) are extensively applied in critical fields such as aviation,semiconductor,biomedicine,and other key fields due to their excellent material properties.However,traditional machining technologies often struggle to achieve ultra-precision with DMMs resulting from poor surface quality and low processing efficiency.In recent years,field-assisted machining (FAM) technology has emerged as a new generation of machining technology based on innovative principles such as laser heating,tool vibration,magnetic magnetization,and plasma modification,providing a new solution for improving the machinability of DMMs.This technology not only addresses these limitations of traditional machining methods,but also has become a hot topic of research in the domain of ultra-precision machining of DMMs.Many new methods and principles have been introduced and investigated one after another,yet few studies have presented a comprehensive analysis and summarization.To fill this gap and understand the development trend of FAM,this study provides an important overview of FAM,covering different assisted machining methods,application effects,mechanism analysis,and equipment design.The current deficiencies and future challenges of FAM are summarized to lay the foundation for the further development of multi-field hybrid assisted and intelligent FAM technologies.

Study of the material removal mechanism of glass-ceramics based on consecutive incremental loading in ductile-regime grinding

Glass-ceramics have many excellent properties and are widely used in various fields. During the grinding process,the workpiece surface is typically subject to material removal by grit of incremental heights, which has rarely been the focus of research. As such, it is necessary to study the material removal mechanism of glass-ceramics under consecutive incremental loading, which more closely reflects the actual grinding process. In this paper,to analyze the plastic deformation and residual stress of lithium aluminosilicate(LAS) glass-ceramics, a finite element model is established based on the Drucker–Prager yield criterion for ductile regimes. A nano-scratch test was also conducted and the test results show that both the residual depth and residual stress increase with an increase in the number of increments, and that consecutive incremental loading promotes the plastic deformation of glass-ceramics and increases the residual stress of the material in the ductile-regime process. These findings provide guidance for achieving higher dimensional accuracy in the actual grinding of glass-ceramics parts.

Molecular dynamics simulation of the material removal in the scratching of 4H-SiC and 6H-SiC substrates

Single crystal silicon carbide(SiC)is widely used for optoelectronics applications.Due to the anisotropic characteristics of single crystal materials,the C face and Si face of single crystal SiC have different physical properties,which may fit for particular application purposes.This paper presents an investigation of the material removal and associated subsurface defects in a set of scratching tests on the C face and Si face of 4H-SiC and 6H-SiC materials using molecular dynamics simulations.The investigation reveals that the sample material deformation consists of plastic,amorphous transformations and dislocation slips that may be prone to brittle split.The results showed that the material removal at the C face is more effective with less amorphous deformation than that at the Si face.Such a phenomenon in scratching relates to the dislocations on the basal plane(0001)of the SiC crystal.Subsurface defects were reduced by applying scratching cut depths equal to integer multiples of a half molecular lattice thickness,which formed a foundation for selecting machining control parameters for the best surface quality.

Electrolyte composition and removal mechanism of Cu electrochemical mechanical polishing

The optimization of electrolytes and the material removal mechanisms for Cu electrochemical mechanical planarization(ECMP)at different pH values including 5-methyl-1H-benzotriazole(TTA),hydroxyethylidenediphosphoric acid(HEDP),and tribasic ammonium citrate(TAC)were investigated by electrochemical techniques,X-ray photoelectron spectrometer(XPS)analysis,nano-scratch tests,AFM measurements,and polishing of Cu-coated blanket wafers.The experimental results show that the planarization efficiency and the surface quality after ECMP obtained in alkali-based solutions are superior to that in acidic-based solutions,especially at pH=8.The optimal electrolyte compositions(mass fraction)are 6% HEDP,0.3% TTA and 3% TAC at pH=8.The main factor affecting the thickness of the oxide layer formed during ECMP process is the applied potential.The soft layer formation is a major mechanism for electrochemical enhanced mechanical abrasion.The surface topography evolution before and after electrochemical polishing(ECP)illustrates the mechanism of mechanical abrasion accelerating electrochemical dissolution,that is,the residual stress caused by the mechanical wear enhances the electrochemical dissolution rate.This understanding is beneficial for optimization of ECMP processes.

Effect of tool geometry on ultraprecision machining of soft-brittle materials:a comprehensive review

Brittle materials are widely used for producing important components in the industry of optics,optoelectronics,and semiconductors.Ultraprecision machining of brittle materials with high surface quality and surface integrity helps improve the functional performance and lifespan of the components.According to their hardness,brittle materials can be roughly divided into hard-brittle and soft-brittle.Although there have been some literature reviews for ultraprecision machining of hard-brittle materials,up to date,very few review papers are available that focus on the processing of soft-brittle materials.Due to the‘soft’and‘brittle’properties,this group of materials has unique machining characteristics.This paper presents a comprehensive overview of recent advances in ultraprecision machining of soft-brittle materials.Critical aspects of machining mechanisms,such as chip formation,surface topography,and subsurface damage for different machining methods,including diamond turning,micro end milling,ultraprecision grinding,and micro/nano burnishing,are compared in terms of tool-workpiece interaction.The effects of tool geometries on the machining characteristics of soft-brittle materials are systematically analyzed,and dominating factors are sorted out.Problems and challenges in the engineering applications are identified,and solutions/guidelines for future R&D are provided.

The technology and mechanism of removal of plastic mulch and land preparation

In this article,the characteristic of the field plastic mulch, the craft for mechanization removal and land preparation of plastic mulch and the mechanism frequently used in the removal and land preparation of plastic mulch were introduced, which offered references for the design of removal mechanism and land preparation of plastic mulch and structural optimization combination of working components.

A Comparative Study on the Efficacy between Minimally Invasive Caries Removal Technique involving Carisolv and Traditional Mechanical Caries Removal in Treating Dental Caries in Children

Objective:To explore the curative effect of Carisolv,a minimally invasive caries removal technique and traditional mechanical caries removal treatment on children’s dental caries.Methods:A total of 97 children with dental caries who were treated in the Department of Stomatology in Affiliated Hospital of Chifeng University,Chifeng from September 2017 to May 2019 were selected and recruited as the research subjects.They were divided into two groups by random number table method.Forty-nine individuals were assigned in the control group while the remaining 48 individuals in the observation group.The control group was treated with traditional mechanical caries removal method,and the observation group was treated with minimally invasive caries removal technique,i.e.Carisolv.Both groups were followed up for six months.The degree of pain,recovery time of dental function and complications after six months of treatment were observed in the two groups of children.Results:During the treatment,compared with the control group,the children in the observation group experienced lower degree of pain and had shorter recovery time of dental function.After six months of treatment,the incidence of complications in the observation group was lower than that in the control group.The difference was statistically significant(P<0.05).Conclusion:Compared with traditional mechanical caries removal method,Carisolv,a minimally invasive caries removal technique could reduce the pain of children during the treatment process,shorten the time to restore dental function,reduce the occurrence of complications,and had a better therapeutic effect in treating children’s dental caries.

Modeling and analysis for material removal and surface roughness in fluid jet polishing of optical glass

luid jet polishing(FJP)is a non-contact polishing technology that can fabricate free-form optical surfaces with sub-micron-level form accuracy and nano-level surface roughness,especially for hard and brittle materials.The surface generation model of FJP can be used to guide the determination and optimization of process parameters and is of great significance for understanding the evolution mechanism of surface microtopography.However,predictive models for the microscopic topography of polished surfaces are still lacking.This study established a macroscopic surface profile model for predicting 3D material removal characteristics and surface texture by combining the 3D computer fluid dynamics(CFD)simulation model and single-particle erosion mechanism.A fractal theory-based erosion model has been built to calculate the material removal caused by the erosion of a single abrasive particle on the rough surface;thus,it predicts the micro-topography and surface roughness of the polished samples.A series of polishing experiments were conducted to analyze the feasibility and accuracy of the model quantitatively and study the influence mechanism of process parameters on the material removal characteristics and surface quality.Results indicated that the models could well predict material removal and surface roughness.The prediction accuracy of the surface roughness Ra and maximum removal depth is better than 91.6%and 90%,respectively.It is also found that the material removal rate of FJP could reach 0.517 mm3/min,and the surface roughness convergence rate could reach 62.9%.

Membrane modification in enhancement of virus removal:A critical review

Many waterborne diseases are related with viruses,and COVID-19 worldwide has raised the concern of virus security in water into the public horizon.Compared to other conventional water treatment processes,membrane technology can achieve satisfactory virus removal with fewer chemicals,and prevent the outbreaks of viruses to a maximal extent.Researchers developed new modification methods to improve membrane performance.This review focused on the membrane modifications that enhance the performance in virus removal.The characteristics of viruses and their removal by membrane filtration were briefly generalized,and membrane modifications were systematically discussed through different virus removal mechanisms,including size exclusion,hydrophilic and hydrophobic interactions,electronic interactions,and inactivation.Advanced functional materials for membrane modification were summarized based on their nature.Furthermore,it is suggested that membranes should be enhanced through different mechanisms mainly based on their ranks of pore size.The current review provided theoretical support regarding membrane modifications in the enhancement of virus removal and avenues for practical application.

Removal performance,mechanisms,and influencing factors of biochar for air pollutants:a critical review

The emission of air pollutants from various industries is a major contributor to environmental pollution.The removal of these pollutants before they are discharged into the environment has become an important means of controlling air pollution.Biochar has attracted increasing attention because of its low cost,high porosity,large specific surface area,abundant surface functional groups,and high removal capacity.The physicochemical properties of biochar are greatly affected by feedstock types,preparation,and modification conditions.For this reason,the capacity and propensity of biochar for removing air pollutants are rather variable.To understand the existing research status and grasp the latest research progress,a systematic review on the removal of different air pollutants by biochar is highly needed.Based on the recent research,this paper systematically analyzes and summarizes the preparation and modification methods of biochar commonly used for the removal of six air pollutants(SO_(2),H_(2)S,CO_(2),Hg0,VOCs,and NH_(3)),as well as the removal performance and mechanisms.Then,the potential influencing factors(preparation parameters,physicochemical characteristics of biochar,and removal conditions)are discussed.Finally,the regeneration of biochar,suggestions,and future perspectives are proposed.

Precision Grinding of Reaction Bonded Silicon Carbide Using Coarse Grain Size Diamond Wheels

Reaction bonded SiC（RBSiC） is attractive for optical application because of its favorable properties and low fabrication cost. However, the difficultness and cost involved in RBSiC grinding limit its application. The investigation on high efficient and low-cost machining with good grinding quality is desired. Generally, high efficient machining for RBSiC is realized by using coarse grain size grinding wheels, but serious grinding damage is inevitable. In this paper, monolayer nickel electroplated coarse grain size diamond grinding wheels with grain sizes of 46 μm, 91 μm, and 151 μm were applied to the grinding of RBSiC. An electrolytic in-process dressing（ELID） assisted conditioning technique was first developed by using cup shape copper bonded conditioning wheels with grain sizes of 15 μm and 91 μm to generate the conditioned coarse grain size wheels with minimized wheel run-out error within 2 μm, constant wheel peripheral envelop as well as top-flattened diamond grains. Then, the grinding experiments on RBSiC were carried out to investigate the grinding performance and material removal mechanism. The experimental results indicate that the developed conditioning technique is applicable and feasible to condition the coarse grain size diamond wheels under optimal conditioning parameters, and the material removal mechanism involved in RBSiC grinding is the combination of brittle fracture and ductile deformation to generate smooth ground surface. This research is significant for the high efficient and low-cost precision grinding of RBSiC with good ground surface quality.

Assessing ability of a wet swale to manage road runoff：A case study in Hefei, China

The ability of a wet swale,constructed in an area of poor soil permeability,to manage runoff from a roadway was monitored through 27 storm events over a period of 8 months.During the monitoring period,the wet swale reduced the total runoff volume by 50.4%through exfiltration and evapotranspiration.The wet swale significantly decreased the influent pollutant concentrations,and the effluent mean concentrations of total suspended solids,total phosphorus,chemical oxygen demand,ammonium,oxidized nitrogen,and total nitrogen in the effluent were 31 mg/L,0.10 mg/L,29 mg/L,0.52 mg/L,0.35 mg/L and1.28 mg/L,respectively.Pollutant loads were also substantially reduced from 70%to 85%.Plant uptake played an important role in nutrient removal in the wet swale.Approximately half of the nitrogen(53.8%)and phosphorus(51.5%)that entered the wet swale was incorporated in above-ground plants.It is shown that wet swales are useful for managing runoff from roads in areas of poor soil permeability.

Mechanism of ultrasonic-pulse electrochemical compound machining based on particles

The electric double layer with the transmission of particles was presented based on the principle of electrochemistry.In accordance with this theory,the cavitation catalysis removal mechanism of ultrasonic-pulse electrochemical compound machining(UPECM) based on particles was proposed.The removal mechanism was a particular focus and was thus validated by experiments.The principles and experiments of UPECM were introduced,and the removal model of the UPECM based on the principles of UPECM was established.Furthermore,the effects of the material removal rate for the main processing parameters,including the particles size,the ultrasonic vibration amplitude,the pulse voltage and the minimum machining gap between the tool and the workpiece,were also studied through UPECM.The results show that the particles promote ultrasonic-pulse electrochemical compound machining and thus act as the catalyzer of UPECM.The results also indicate that the processing speed,machining accuracy and surface quality can be improved under UPECM compound machining.

Plasma-enabled electrochemical jet micromachining of chemically inert and passivating material

Electrochemical jet machining(EJM)encounters significant challenges in the microstructuring of chemically inert and passivating materials because an oxide layer is easily formed on the material surface,preventing the progress of electrochemical dissolution.This research demonstrates for the first time a jet-electrolytic plasma micromachining(Jet-EPM)method to overcome this problem.Specifically,an electrolytic plasma is intentionally induced at the jet-material contact area by applying a potential high enough to surmount the surface boundary layer(such as a passive film or gas bubble)and enable material removal.Compared to traditional EJM,introducing plasma in the electrochemical jet system leads to considerable differences in machining performance due to the inclusion of plasma reactions.In this work,the implementation of Jet-EPM for fabricating microstructures in the semiconductor material 4H-SiC is demonstrated,and the machining principle and characteristics of Jet-EPM,including critical parameters and process windows,are comprehensively investigated.Theoretical modeling and experiments have elucidated the mechanisms of plasma ignition/evolution and the corresponding material removal,showing the strong potential of Jet-EPM for micromachining chemically resistant materials.The present study considerably augments the range of materials available for processing by the electrochemical jet technique.

High Efficiency Axial Deep Creep-Feed Grinding Machining Technology of Engineering Ceramics Materials

Axial deep creep-feed grinding machining technology is a high efficiency process method of engineering ceramics materials, which is an original method to process the cylindrical ceramics materials or hole along its axis. The analysis of axial force and edge fracture proved the cutting thickness and feed rate could be more than 5-10 mm and 200 mm/min respectively in once process, and realized high efficiency, low-cost process of engineering ceramics materials. Compared with high speed-deep grinding machining, this method is also a high efficiency machining technology of engineering ceramics materials as well as with low cost. In addition, removal mechanism analyses showed that both median/radial cracks and lateral cracks appeared in the part to be removed, and the processed part is seldom destroyed, only by adjusting the axial force to control the length of transverse cracks.