Non-thermal Plasma Irradiation Research Articles

Harnessing the power of nonthermal Plasma: A breakthrough in stabilizing Thallium contaminants in soil and unveiling the mechanism

Thallium (Tl) is a highly toxic element and can accumulate in human body through food, water, or air and cause damage to multiple organs. In this study, the nonthermal plasma (NTP) was employed to irradiate the potassium dihydrogen phosphate (KH2PO4) and sodium diethyldithiocarbamate trihydrate (SDDC) to solve the issues brought by their poor stability and insufficient chelation capabilities in soils to intensify their performance on immobilizing monovalent Tl contaminants in soils. Both an orthogonal design (OD) and a central composite design (CCD) were adopted to arrange the multi-parametrical modification and stabilization experiments. The leaching toxicities ranging from 5.11 to 52.37 µg/L of Tl+ ions were obtained in the OD experiments. The changes in both NTP time and the molar ratios of KH2PO4 to SDDC had a significant effect on the activation procedure. The leaching concentration ranging from 0.37 to 7.34 µg/L was achieved in the CCD stabilization experiments. NTP activation and the rearrangement of the stabilization conditions both were beneficial to the transformation of physicochemical states of Tl pollutants in soils, which proved the existence of chemical immobilization brought by the irradiated stabilizers (NTP-PK-SDDCs) to the Tl contaminants. The stabilization process was targeted between only Tl contaminants and NTP-PK-SDDCs in soils. The NTP irradiation enhanced the physicochemical characteristics of stabilizers, further intensifying the immobilization of Tl species in the soils. The enhancement mechanism was attributed to the free radicals-induced doping, oxidation, and polycondensation and the bombards of electrons, which strengthened the electrostation and chemisorption of NTP-PK-SDDCs towards Tl ions. The potential impact of this study includes the development of more effective and sustainable remediation methods for Tl-contaminated soils, contributing to environmental protection and human health.

Synthesis of nonthermal plasma-irradiated polyvalent manganese (hydro)oxide functionalized nanosilica for intensifying geopolymerized solidification/stabilization of thallium-contaminated soil and mechanism exploration

Thallium (Tl) enrichment in soils can cause an immeasurable ecological disaster, disturbing ecological balance and threatening human health. In this study, nonthermal plasma (NTP) irradiation was employed to synthesize polyvalent Mn-based (hydro)oxide-functionalized nanosilica (NTP-P-Mn-nSi). Mixtures of alkali-activated geopolymers and NTP-P-Mn-nSi were subsequently prepared for the efficient solidification and stabilization (S/S) of Tl-containing soils. The synthesis of NTP-P-Mn-nSi and the geopolymerization of soils were both optimized to obtain maximum adsorption capacities and achieve excellent immobilization of the matrix. The influence of the initial pH and concentration of Tl+ on NTP-P-Mn-nSi was investigated. The leaching concentration of Tl and the compressive strengths from the soil matrix were monitored. Comprehensive strategies were adopted for soils and solidified samples to investigate the vital role played by NTP-P-Mn-nSi in the geopolymers of soils. The pseudofirst-order, intraparticle, and Elovich models were suitable for evaluating the uptake dynamics of Tl+ to NTP-P-Mn-nSi. Langmuir, Freundlich, and Tempkin were all appropriate in analysing the isotherms of heterogeneous adsorption. Four maximum monolayer adsorption capacities of NTP-P-Mn-nSi responding to Tl+ ions reached 93.90, 123.00, 355.87, and 323.62 mg/g at initial pH values of 7, 9, 11, and 13, respectively. NTP-P-Mn-nSi in the geopolymer explicitly inhibited leaching and intensified the immobilization of Tl ions in the matrix with the lowest leaching concentration of 0.16 µg/L Tl from the matrix being achieved. The increase in NTP-P-Mn-nSi dosage accelerated the growth rates of nucleation, enhanced the formation of alkali-activated gelation, induced the formation of flocculent surfaces and three-dimensional structures, and intensified the elemental overlap between Mn and Tl in the geopolymerized matrix.

Self-cementation of gold tailings activated by nonthermal plasma irradiated calcium (hydro)oxide

The alkalinity of CaO is commonly insufficient in alkali-activating raw soils or minerals for the formation of cementation or geopolymerization. In this study, nonthermal plasma (NTP) irradiation was employed to activate traditional CaO to enhance its efficacy in alkali activation and further intensify the self-cementation of gold tailings. The solidification/stabilization (S/S) of the gold tailings-based matrix activated by NTP-CaO was better than that of CaO. The NTP irradiation enhanced the surface hydroxyl groups and oxygen atoms, decreased the binding energy, formed nanoparticles, and significantly changed the morphologies of the calcium activator. The dosage of the NTP-irradiated CaO (NTP-CaO) directly affected the self-cemented solidification/stabilization of gold tailings. The Johnson-Mehl-Avrami–Kolmogorov model was appropriate for analysing the NTP-CaO-activated geopolymerization kinetics of gold tailings. Three-dimensional (3D) structural minerals covered with small pores were determined in the NTP-CaO-activated cemented samples. The employment of NTP-CaO facilitated the formation of aluminosilicate geopolymers during the self-cementation of gold tailings according to comprehensive characterization strategies. The study achieves the efficient self-remediation of gold tailings by activating calcium precursors, which further solves the contradiction between salinization and alkali activation in the field of noncalcined cementitious materials.

Nonthermal plasma-irradiated polyvalent ferromanganese binary hydro(oxide) for the removal of uranyl ions from wastewater

Nonthermal plasma (NTP) irradiation was employed to adjust the morphological structures and valence distribution of ferromanganese (Fe–Mn)-based binary hydro (oxide) to enhance the heterogeneous adsorption of uranyl ions. The output voltage and the liquid-plate distance played a more vital role among the NTP factors in the irradiation system in influencing the polyvalent Fe–Mn binary hydro (oxide) (poly-Fe-Mn). The formation of plates, flakes, and nanoscale nodules was specifically observed, which caused more pores and fractures in the poly-Fe-Mn binary hydro (oxide). The poly-Fe-Mn performed explicitly better in the adsorption of uranium ions in comparison with the counterpart of the Fe–Mn, which was appropriately fitted by the pseudofirst-order kinetic and Elovich models. Maximum equilibrium adsorption capacities of 663.92 and 923.45 mg/g were obtained for the Fe–Mn and poly-Fe-Mn binary hydro (oxides) toward U ions in the orthogonal design, respectively. The maximum monolayer adsorption capacity achieved by the fitting of the Langmuir model was 1091.10 mg/g. Both physisorption and chemisorption contributed to the heterogeneous process of the poly-Fe-Mn toward uranium ions. The employment of NTP irradiation changed the monolayer adsorption of the traditional Fe–Mn materials and diversified the reaction mechanisms between the interface of the Fe–Mn materials and uranium ions. The elements, including O, N, and U exhibited higher compatibility and overlapped in the samples. The highly effective capture of uranium ions from the solution by the poly-Fe-Mn binary hydro (oxide) was mainly related to the chemical deposition of O and N radicals.

Cooperative Catalysis of Vibrationally Excited CO2 and Alloy Catalyst Breaks the Thermodynamic Equilibrium Limitation

Using nonthermal plasma (NTP) to promote CO2 hydrogenation is one of the most promising approaches that overcome the limitations of conventional thermal catalysis. However, the catalytic surface reaction dynamics of NTP-activated species are still under debate. The NTP-activated CO2 hydrogenation was investigated in Pd2Ga/SiO2 alloy catalysts and compared to thermal conditions. Although both thermal and NTP conditions showed close to 100% CO selectivity, it is worth emphasizing that when activated by NTP, CO2 conversion not only improves more than 2-fold under thermal conditions but also breaks the thermodynamic equilibrium limitation. Mechanistic insights into NTP-activated species and alloy catalyst surface were investigated by using in situ transmission infrared spectroscopy, where catalyst surface species were identified during NTP irradiation. Moreover, in in situ X-ray absorption fine-structure analysis under reaction conditions, the catalyst under NTP conditions not only did not undergo restructuring affecting CO2 hydrogenation but also could clearly rule out catalyst activation by heating. In situ characterizations of the catalysts during CO2 hydrogenation depict that vibrationally excited CO2 significantly enhances the catalytic reaction. The agreement of approaches combining experimental studies and density functional theory (DFT) calculations substantiates that vibrationally excited CO2 reacts directly with hydrogen adsorbed on Pd sites while accelerating formate formation due to neighboring Ga sites. Moreover, DFT analysis deduces the key reaction pathway that the decomposition of monodentate formate is promoted by plasma-activated hydrogen species. This work enables the high designability of CO2 hydrogenation catalysts toward value-added chemicals based on the electrification of chemical processes via NTP.

Salt-free and low temperature colouration of silk using He–N2 non-thermal plasma irradiation

A natural protein fibre (silk), in the form of textile, was subjected to a non-thermal plasma irradiation in a mixture of helium/nitrogen (He–N2) gases by varying the nitrogen (N2) gas flow rates at atmospheric pressure. After 4 min He–N2 plasma irradiation, the silk fabric was found to be more hydrophilic in nature in terms of decrease in time of water absorbency. A similar improvement was also noticed with an increase in both the plasma irradiation time and N2 gas flow rate. The scanning electron micrographs (SEM) of the treated samples depicted the etching of fibre surface and occurrence of micro-pits and craters. The energy dispersive X-ray (EDX) elemental analysis depicted maximum 2.2% and 2.9% increase in oxygen (O2) and nitrogen (N2), respectively owing to plasma-induced chemical change in the silk protein fibre. Mass spectroscopy results also exhibited an improvement in amine, amide, imine and other polar groups in the plasma irradiated samples, which caused them to be dyeable with acid dye without usage of salt, even at a much lower temperatures of 40 °C and 60 °C compared to conventionally used 90 °C. The rate of dyeing in the plasma pre-irradiated silk was found to improve more than 50% and 30% compared to that of the untreated silk fabric dyed at 40 °C and 60 °C, respectively. The improvements in dye absorption, dye-fixation, and colour strength were measured in details with variable gas flow rates and correlated with the changes in surface physico-chemical properties of silk polymer. It is postulated that the enhancement in surface roughness along with formation of hydrophilic groups on the fibre surface contributed towards the observed improvements. In the plasma treated dyed samples, colour stability towards the washing, rubbing and light exposure was 1–2 grades higher as compared to that in case of untreated sample. The proposed low-temperature and salt-free process will economise the cost of colouration of silk fabric, besides reducing the effluent load.

Enhanced ability of plasma-activated lactated Ringer's solution to induce A549 cell injury

Non-thermal plasma (NTP) is applicable to living cells and has emerged as a novel technology for cancer therapy. Plasma-activated medium (PAM), which is prepared by the irradiation of culture medium with NTP, induces cell death in cancer cells. However, difficulties are associated with applying PAM to the clinical phase because culture media cannot be used for medical treatments. The objectives of the present study were to demonstrate the inhibitory effects of plasma-activated lactated Ringer's solution (PAL) on the viability of the A549 cancer cell line and elucidate the underlying mechanisms. The anti-tumor activity of PAL was significantly stronger than that of PAM, whereas their concentrations of H2O2 and nitrite were similar. Lactated Ringer's solution (Lac-R) consists of lactate and three types of inorganic salts. The results showing that NTP irradiation of the lactate solution rather than the inorganic salt solution induced the inactivation of catalase were dependent on the presence or absence of nitrite in these solutions. We detected nitrotyrosine in A549 cells treated with PAM or PAL, and the addition of catalase to PAM rather than to PAL reduced its production. The PAL treatment of A549 cells led to mitochondrial dysfunction with the down-regulation of NF-κB-Bcl2 signaling.

Contribution Of Intracellular Mobile Zinc To Anti-Cancer Effects Of Plasma-Activated Medium

Non-thermal plasma (NTP) irradiation has been reported to have a broad array of biological effects, and has been found to preferentially kill cancer cells. Therefore, NTP is a promising approach for cancer therapy. The indirect NTP irradiation method using plasma-activated medium (PAM) induces cancer cell death to the same extent as the direct NTP irradiation method. The anti-cancer effects of PAM are thought to be attributed to reactive oxygen species (ROS), mainly H2O2. On the other hand, oxidative stress caused by ROS has been demonstrated to induce the liberation of zinc (Zn2+) from intracellular Zn2+ pools and Zn2+-dependent cell death. Zn2+ is thought to function as a second messenger activated by oxidative stress. We previously reported that PAM rapidly triggered intracellular Zn2+ liberation in human neuroblastoma SH-SY5Y cells, and that the liberated Zn2+ induced activation of poly(ADP-ribose) polymerase 1 (PARP-1) and subsequent loss of cellular NAD+ and ATP, resulting in cell death associated with energy exhaustion. Recently, we also found that normal human fibroblasts were less sensitive to PAM cytotoxicity compared with SH-SY5Y cells. PAM decreased intracellular NAD+ levels in both cell types, whereas the depletion of ATP and mitochondrial ROS generation were hardly observed in fibroblasts. The addition of Zn2+ augmented PAM-induced cell death and ATP depletion in fibroblasts. The levels of PAM-induced Zn2+ liberation were lower in fibroblasts than in SH-SY5Y cells. These findings suggest the possibility that cells with high intracellular mobile Zn2+ are susceptible to PAM cytotoxicity. Moreover, PAM promoted G2/M growth arrest of lung adenocarcinoma A549 cells via activation of the ATM-p53 pathway and the Zn2+ chelator N,N,N',N'-tetrakis(2-pyridylmethyl)ethylenediamine (TPEN) suppressed these events. Thus, we consider intracellular mobile Zn2+ to play a key role in the anti-cancer effects of PAM.

Bactericidal Action Mechanism of Nonthermal Plasma: Denaturation of Membrane Proteins

With increasing attention in indoor air quality for human health, control of microbial contaminants has gained interest. In an attempt to develop an efficient way to control pathogenic microbes in ambient air, an air-purification technology using nonthermal plasma (NTP) has been developed. However, there is no obvious study on bactericidal mechanism even though the NTP irradiation results in bacterial cell death. In this paper, the fluorescent-based bacterial viability assay indicates that the NTP irradiation resulted in the denaturation of bacterial membrane proteins. In addition, the analysis of 2-D electrophoresis and peptide mass fingerprinting reveal that bacterial proteins are denatured by the treatment. Based on these results, we proposed a possible inactivation mechanism of NTP irradiation, emphasizing the important role of the reaction between positive and negative ions generated by NTP and pointing consequent denaturation of bacterial membrane proteins. This paper will contribute to a better understanding of the bactericidal mechanism by the NTP irradiation.

Selective uptake of epidermal growth factor-conjugated gold nanoparticle (EGF-GNP) facilitates non-thermal plasma (NTP)-mediated cell death

Non-thermal atmospheric pressure plasma (NTP) has been shown to induce cell death in various mammalian cancer cells. Accumulated evidence also shows that NTP could be clinically used in cancer therapy. However, the current NTP-based applications lack target specificity. Here, a novel method in NTP-mediated cancer therapeutics was described with enhanced target specificity by treating EGF (epidermal growth factor)-conjugated GNP (gold nanoparticle). The treatment with EGF-conjugated GNP complex, followed by NTP irradiation showed selective apoptosis of cells having receptor-mediated endocytosis. NTP triggered γ–H2AX elevation which is a typical response elicited by DNA damage. These results suggest that EGF-conjugated GNP functions as an important adjuvant which gives target specificity in applications of conventional plasma therapy.

Real-Time, in Situ Monitoring of Nitric Oxide and Hydrogen Peroxide Generated By Non-Thermal Plasma Irradiation: Use of an Amperometric Microsensor Array

Plasma is high energy electromagnetic radiation. Recently a non-thermal plasma treatment has been employed in emerging new biomedical applications, including bacterial decontamination and chronic wound treatment. Such antimicrobial and healing efficacies may be related to the formation of reactive oxygen and nitrogen species (ROS and RNS; e.g., OH·–, O2·–, NO, ONOO·–, and H2O2) by plasma treatment. Among several reactive species, nitric oxide (NO) has been extensively studied due to its phagocytic and antithrombotic activities, and angiogenic property. In addition, hydrogen peroxide (H2O2), another major species produced by plasma treatment is implicated as the main transmitter of a redox signal in several biological processes. To elucidate bioplasma science, it is essential to real-time, in-situ determine NO and H2O2 produced during plasma treatment and their generation kinetics. Herein we report on a microsensor array to selectively detect NO and H2O2 generated by non-thermal plasma irradiation, respectively. Two working electrodes (Pt for NO sensing and Pt/aniline derivative for H2O2 sensing, respectively) are modified with a perfluorinated xerogel as a permselective membrane to improve sensor’s selectivities over readily oxidizable interfering species and other ROS and RNS. In addition, the effect of the plasma gas composition (O2/N2 ratio) on NO/H2O2 production ratio will be studied. Finally the microarray sensor will be employed to determine NO and H2O2 generation during plasma irradiation in biological milieu in vivo or ex vivo.

Response of Silkworm Larvae to Atmospheric Pressure Nonthermal Plasma Irradiation

Response of Silkworm Larvae to Atmospheric Pressure Nonthermal Plasma Irradiation

Simple method of improving harvest by nonthermal air plasma irradiation of seeds of Arabidopsis thaliana (L.)

We have studied the effects of air nonthermal plasma irradiation of seeds of Arabidopsis thaliana (L.) on their growth from the beginning of cultivation to their harvest. Three minute plasma irradiation of dry seeds resulted in growth acceleration in all the growth stages. Compared with the control, the plasma irradiation led to an 11% shorter harvest period, a 56% increase in total seed weight, a 12% increase in each seed weight, and a 39% increase in seed number.

Non-thermal plasma mills bacteria: Scanning electron microscopy observations

Non-thermal plasmas hold great promise for a variety of biomedical applications. To ensure safe clinical application of plasma, a rigorous analysis of plasma-induced effects on cell functions is required. Yet mechanisms of bacteria deactivation by non-thermal plasma remain largely unknown. We therefore analyzed the influence of low-temperature atmospheric plasma on Gram-positive and Gram-negative bacteria. Using scanning electron microscopy, we demonstrate that both Gram-positive and Gram-negative bacteria strains in a minute were completely destroyed by helium plasma. In contrast, mesenchymal stem cells (MSCs) were not affected by the same treatment. Furthermore, histopathological analysis of hematoxylin and eosin–stained rat skin sections from plasma–treated animals did not reveal any abnormalities in comparison to control ones. We discuss possible physical mechanisms leading to the shred of bacteria under non-thermal plasma irradiation. Our findings disclose how helium plasma destroys bacteria and demonstrates the safe use of plasma treatment for MSCs and skin cells, highlighting the favorability of plasma applications for chronic wound therapy.

Denaturation of Cytochrome C Induced by Non-Thermal Plasma Irradiation

Cytochrome c, a heme protein located in mitochondria of cell, has the electron transport function for it undergoes oxidation/reduction to transfer electrons between cytochrome c reductase and cytochrome c oxidase. Due to its location and function, cytochrome c is also a target of reactive oxygen species (ROS) in cells since mitochondria are the main place producing intracellular ROS. Because ionizing radiation can elicit significant ROS enhancement in cells, investigating the radiation-induced oxidative damage of cytochrome c is therefore an interesting issue. So far there have been some literatures reporting the oxidative damage of cytochrome c by ROS [1-3], but most of them focused on the modification of peptide moiety. In this work, non-thermal plasma [4] was employed to induce the oxidative damage on cytochrome c. Various oxidants including free radicals such as hydroxyl radical, superoxide radical and hydrogen peroxide were produced in solution during the plasma discharge. It was found that the protein was rapidly denatured/degraded by plasma discharge. By adding ROS scavengers it was confirmed that hydrogen peroxide was the main direct factor leading to the enzyme's denaturation. The results make us better understand the process and mechanism for the enzyme's oxidative damage and therefore may help us to find ways to protect cells from damage under oxidative stress conditions.This work was supported by the Foundation of the Natural Science of China (No.10975152), Hundred Talents Program of Chinese Academy of Sciences (CAS) and the Key Knowledge Innovation Project of CAS.[1] J. Kim et al., Free Radic Biol Med. 2008, 44, 1700-1711.[2] W. S. Zong, et al., Spectrochimica Acta Part A 2011, 78, 1581-1586.[3] N. H. Kim, et al., Mol. Cells, 2006, 22, 220-227.[4] Z. Ke, et al., Plasma Processes and Polymers (in press)