Non-thermal Plasma Modification Research Articles

Surface optimization of nanodiamonds using non-thermal plasma

Sensitive local monitoring of intracellular processes by quantum sensing utilizing nitrogen-vacancy (NV) centers in nanodiamonds (NDs), would greatly advance cell biology and medicine. However, NDs still fall behind in sensitivity compared to bulk diamond because of their much shorter NV relaxation times. As suggested in theoretical studies, prolongation of NV relaxation times should be achievable by surface optimization creating mixed H/O surface termination consisting of hydrogen atoms, hydroxyl groups, and C–O–C ether bridges. Here we target such chemistry by employing a non-thermal plasma (NTP) in a point-to-plain discharge configuration in aqueous solution. We have devised a set of experiments with different types of nanodiamond samples (of HPHT or detonation origin and with an H- or O-terminated surface) and four working gases (air, O2, He, and H2). Using FTIR, we have found that NTP modification induces a relative increase of O–H and C–H bonds with respect to CO bonds. We have observed the biggest changes in FTIR spectra and the greatest decrease in zeta potential with oxidized NDs (both detonation and HPHT) and hydrogen as the working gas. NV electron spin relaxation times of thus modified HPHT NDs indicate an improvement of the T1 time by ∼17%–∼29% and the T2 time prolongation of 40%.

Electrospun microcrystalline cellulose/chitosan porous composite nanofibrous membranes modified by non-thermal plasma for gaseous formaldehyde adsorption

To develop a green and facile adsorbent for removing indoor polluted formaldehyde (HCHO) gas, the biomass porous nanofibrous membranes (BPNMs) derived from microcrystalline cellulose/chitosan were fabricated by electrospinning. The enhanced chemical adsorption sites with diverse oxygen (O) and nitrogen (N)-containing functional groups were introduced on the surface of BPNMs by non-thermal plasma modification under carbon dioxide (CO2) and nitrogen (N2) atmospheres. The average nanofiber diameters of nanofibrous membranes and their nanomechanical elastic modulus and hardness values decreased from 341 nm to 175–317 nm and from 2.00 GPa and 0.25 GPa to 1.70 GPa and 0.21 GPa, respectively, after plasma activation. The plasma-activated nanofibers showed superior hydrophilicity (WCA = 0°) and higher crystallinity than that of the control. The optimal HCHO adsorption capacity (134.16 mg g−1) of BPNMs was achieved under a N2 atmosphere at a plasma power of 30 W and for 3 min, which was 62.42 % higher compared with the control. Pyrrolic N, pyridinic N, CO and O–C=O were the most significant O and N-containing functional groups for the improved chemical adsorption of the BPNMs. The adsorption mechanism involved a synergistic combination of physical and chemical adsorption. This study provides a novel strategy that combines clean plasma activation with electrospinning to efficiently remove gaseous HCHO.

Structural evolution and catalytic mechanism of the non-thermal plasma modified Pd/Al2O3 in C2H6 catalytic combustion

Catalytic combustion of C2H6 at equivalence ratios of 1.0 and 1.4 over non-thermal plasma (NTP) modified Pd/Al2O3 was studied experimentally to examine the effect of O2 and N2 plasma on the catalyst activity and physico-chemical property. C2H6 conversion, chemical product distribution and selectivity were taken into account to evaluate the performance of modified catalysts in C2H6 oxidation at 200–500 ℃. The results showed that the plasma modification had suppressive effects on the activity of Pd/Al2O3. When compared to Pd/Al2O3, T30 for the modified Pd/Al2O3 were shifted to higher temperatures by approximately 30–50 ℃. For catalysts modified by plasma, significantly more CO was formed in the C2H6 combustion at high temperature region. Moreover, the structure, morphology and chemical states of Pd/Al2O3 after modification were thoroughly analyzed with the means of N2 adsorption–desorption, XRD, XPS and SEM. The surface area of modified catalysts decreased, resulting in the activity degradation. The leaching of Pd species and transform of γ-Al2O3 to θ-Al2O3 were observed after the NTP treatment with highly energetic electrons. It should to be highlighted that the reduction of Pd2+ to Pd0 by NTP modification on the catalyst surface from XPS analysis. The NTP had the potential to reduce catalysts while employing oxidizing or inert gases.

Cu/TiO2 adsorbents modified by air plasma for adsorption–oxidation of H2S

In this study, non-thermal plasma (NTP) was employed to modify the Cu/TiO2 adsorbent to efficiently purify H2S in low-temperature and micro-oxygen environments. The effects of Cu loading amounts and atmospheres of NTP treatment on the adsorption-oxidation performance of the adsorbents were investigated. The NTP modification successfully boosted the H2S removal capacity to varying degrees, and the optimized adsorbent treated by air plasma (Cu/TiO2-Air) attained the best H2S breakthrough capacity of 113.29 mg H2S/gadsorbent, which was almost 5 times higher than that of the adsorbent without NTP modification. Further studies demonstrated that the superior performance of Cu/TiO2-Air was attributed to increased mesoporous volume, more exposure of active sites (CuO) and functional groups (amino groups and hydroxyl groups), enhanced Ti-O-Cu interaction, and the favorable ratio of active oxygen species. Additionally, the X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) results indicated the main reason for the deactivation was the consumption of the active components (CuO) and the agglomeration of reaction products (CuS and SO42−) occupying the active sites on the surface and the inner pores of the adsorbents.

Nonthermal Plasma Treatment for Electrocatalysts Structural and Surface Engineering

Structure and surface modification of electrocatalysts demonstrates a promising lead for achieving excellent electrocatalytic activity and efficiency. Among various surface modification strategies, nonthermal plasma technique possesses an irreplaceable role due to the merits of simple but controllable operation procedure, low pollution, low cost, and easy scale‐up for practical applications. Nonthermal plasma treatment, as a powerful tool for material surface and structural engineering, can mainly benefit the electrocatalytic reactions in the following aspects: surface atom doping or reconstructing, introducing vacancies or defects, surface partially reducing or oxidizing, and increasing the porosity or roughness. Given to its flexibility, plasma modification is gaining a noticeable popularity, and great progress has been made in applying plasma for optimizing surface properties of the mainstream electrocatalysts, including metal‐free carbon materials, metal oxides, and other compounds, as well as organometallic electrocatalysts, etc. This review first summarizes the recent advances in nonthermal plasma modification for achieving desirable electrocatalytic behaviors, aiming to highlight the cutting‐edge function designs of electrocatalysts with plasma technology. It is hoped that this work can give some inspiration for the development of highly efficient electrocatalysts.

Impact of Low-Pressure Plasma Treatment of Wool Fabric for Dyeing with PEDOT: PSS.

This study presents the effect of non-thermal plasma modification on the changes of surface morphology, color characteristics and electrical conductivity of wool fabric dyed with intrinsically conductive polymer (ICP) poly (3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT: PSS). The wool fabric was treated with an aqueous dispersion of PEDOT: PSS, Clevios F ET, providing electrically conductive properties to textiles. The wool fabric, containing basic groups of amines (NH2), was pre-activated with low-pressure plasma of non-polymer forming nitrogen (N2) gas before exhaust dyeing with PEDOT: PSS at 90 °C was applied. This treatment imparted hydrophilicity, reduced felting, increased adhesion, improved dye ability and ensured that more PEDOT: PSS negatively charged sulfonate counter ions would be electrostatically bounded with the cationic protonated amine groups of the wool fiber. Initially, before (N2) plasma treatment and after fabrics were evaluated according to the test method for aqueous liquid repellency, the surface morphology of the plasma-modified and -unmodified wool dyed fabric was observed with scanning electron microscopy (SEM). The functional groups introduced onto the surface after N2 gas plasma treatment of wool fabric were characterized by X-ray photoelectron and FTIR-ATR spectroscopy. The results of color difference measurements show that N2 gas plasma treatments provide more intense color on Clevios F ET dyed wool fabric and retain its electrical conductivity.

Modification of hydro-chars by non-thermal plasma to enhance co-anaerobic digestion and degradation of sewage sludge pyrolysis oil

The pyrolysis oil produced from the sewage sludge pyrolysis process is a complex admixture of organic substances, which is difficult to be degraded in a normal anaerobic digestion (AD) process. In this study, the hydro-chars produced at 200, 240, and 280 °C were modified by non-thermal plasma (NTP) and then they were used to promote pyrolysis oil degradation and biogas production in a co-AD digester. The experimental results revealed that after NTP modification, the specific surface areas of the hydro-chars produced at 200 °C (SW200+P) and 240 °C were increased from 28.0 to 39.3 m2g-1 and from 36.2 to 45.4 m2g-1, respectively. Their pore volumes also increased by more than 10%. The SW200+P hydro-char exhibited the highest chemical oxygen demand (COD) removal rate (60.49%) and the highest CH4 yield, which is 6.3 times of the digester with pyrolysis oil but without hydro-char addition (PO + CC). Additionally, the benzene series in the pyrolysis oil can be completely degraded in all digesters with the hydro-char addition. With addition of the SW200+P hydro-char, the Clostridia increased most significantly to become the predominant bacteria community at the class level, and the Methanosarcina became the predominant archaea community at the genus level, which contributed to the increased CH4 yield. The hydro-char addition also increased Dietzia and Cellulosimicrobium, which promoted the degradation of benzene series in the pyrolysis oil. The investigation results suggest that the NTP modification technique can be a potential solution to effectively utilize the hydro-char and help pyrolysis oil degradation via the co-AD process.

Enhancing the Properties of Photocatalysts via Nonthermal Plasma Modification: Recent Advances, Treatment Variables, Mechanisms, and Perspectives

Enhancing the Properties of Photocatalysts via Nonthermal Plasma Modification: Recent Advances, Treatment Variables, Mechanisms, and Perspectives

Doping of nitrogen into biomass-derived porous carbon with large surface area using N2 non-thermal plasma technique for high-performance supercapacitor

A novel and facile modified method using non-thermal plasma is proposed to insert N active sites into biomass-derived porous carbon as high-performance electrode materials for supercapacitor. Large surface areas up to 3040.3 and 2662.5 m2/g with mesopore-dominant hierarchical porous carbons are produced from biomass of lilac and lotus seedpods via KOH activation, respectively. The lilac and lotus seedpods derived porous carbon electrodes present good specific capacitances of 214.5 and 201.1 F/g, respectively. N2 non-thermal plasma modification successfully increases N-containing groups on lilac and lotus seedpods derived porous carbons, where the corresponding N atomic contents are increased by 10.2 and 3.6 times, respectively. As supercapacitor electrodes, their specific capacitances are improved greatly after plasma modification and up to 342.5 F/g (increased by 59.7%) and to 332.1 F/g (increased by 65.2%) at 0.5 A/g in 6 M KOH electrolyte with excellent cycling stability of 85.2% and 95.4% at 10 A/g after 5000 cycles, respectively.

Germination Improvement of Three Pine Species (Pinus) After Diffuse Coplanar Surface Barrier Discharge Plasma Treatment

Seed modification by atmospheric pressure non-thermal plasma treatment was tested on pine species. The Diffuse Coplanar Surface Barrier Discharge (DCSBD) with expose times of 0 s, 1 s, 3 s, 5 s, 10 s, 30 s, 60 s was used on seed treatment of Pinus sylvestris, Pinus nigra and Pinus mugo. The effect of plasma treatment on the chemical bonds on the seed surface was studied using the Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy (ATR-FTIR). Characteristics of seed germination and early growth were measured. ATR-FTIR surface diagnostics did not show any damage. Changes in the peak intensities indicated the presence of oxygen and nitrogen-containing groups, or a reduction of the lipid layer on the surface. Various statistically significant effects of the three species of seeds treated with DCSBD treatment were recorded. No significant differences were found between control sample and plasma treated ones, but some positive trends were obtained. Positive trends were recorded in germinated and growing seeds of all three species mainly after 3 s exposures. Exposure times from 10 s had an inhibitory effect. Based on the results obtained, it can be recommended that forest nurseries performance of nonthermal plasma modification of seeds should be evaluated to measure the durability of the observed growth characteristics.

Enhancement of Cu(II) adsorption on activated carbons by non-thermal plasma modification in O2, N2 and O2/N2 atmospheres

Abstract Activated carbon (AC) was modified by using non-thermal plasma in O2, N2 and O2/N2 atmospheres to increase its Cu(II) adsorption capacity and quantify the influences of the modifying atmospheres. SEM, BET, FT-IR and XPS were used to characterize the surface physical and chemical properties of AC. The results show that the AC modified by using plasma had significantly better Cu(II) adsorption performance than the raw AC. Among the O2, N2 and O2/N2 atmospheres, the AC with plasma modification in N2 showed best Cu(II) adsorption performance and the Cu(II) adsorption capacity was 369.5% higher than the raw AC. The AC modified in O2 atmosphere can form C—COOH groups, while the AC modified in N2 atmosphere can form C—NH2 groups. These two groups are both beneficial for Cu(II) adsorption, where the —NH2 groups are more effective for Cu(II) adsorption compared to —COOH groups. The chemisorption dominated the Cu(II) adsorption on the plasma modified AC and the adsorption performance was dependent on the surface functional groups properties of AC.

Seed Germination of Black Pine (Pinus nigraArnold) After Diffuse Coplanar Surface Barrier Discharge Plasma Treatment

We studied the effects of nonthermal plasma (NTP) treatment on various parameters of early germination stages of Pinus nigra seeds. In the experiment, the diffuse coplanar surface barrier discharge (DCSBD) with treatment time periods of 0, 1, 3, 5, 10, 30, and 60 s was used. Changes on the plasma-treated seed surface were studied by attenuated total reflectance-Fourier transform infrared spectroscopy. Seed germination, germination rate, germination index, length of seedling, dry seedling weight, and seedling vigor index I and II were determined in a growth test under laboratory conditions. Various statistically significant effects of seed exposure to DCSBD plasma treatment were recorded. A positive reaction was observed in the germinated seeds after exposure for 1- and 5-s. Longer exposure time periods had a rather inhibitory effect. The performance of forest nurseries of NTP modification of seeds should be evaluated in order to measure the durability of the observed growth characteristics. The potential of NTP treatment on seeds in plant ecology in future is highlighted.

Adsorption-oxidation of hydrogen sulfide on Fe/walnut-shell activated carbon surface modified by NH3-plasma

Walnut-shell activated carbon (WSAC) supported ferric oxide was modified by non-thermal plasma (NTP), and the removal efficiency for hydrogen sulfide over Fe/WSAC modified by dielectric barrier discharge (DBD) was significantly promoted. The sample modified for 10min and 6.8kV output (30V input voltage) maintained 100% H2S conversion over a long reaction time of 390min. The surface properties of adsorbents modified by NTP under different conditions were evaluated by the methods of X-ray photoelectron spectroscopy (XPS), Brunauer–Emmett–Teller (BET) analysis and in-situ Fourier transform infrared spectroscopy (FTIR), to help understand the effect of the NTP treatment. NTP treatment enhanced the adsorption capacity of Fe/WSAC, which could due to the formation of micro-pores with sizes of 0.4, 0.5 and 0.75nm. XPS revealed that chemisorbed oxygen changed into lattice oxygen after NTP treatment, and lattice oxygen is beneficial for H2S oxidation. From the in-situ FTIR result, transformation of the reaction path on Fe/WSAC was observed after NTP modification. The research results indicate that NTP is an effective method to improve the surface properties of the Fe/WSAC catalyst for H2S adsorption-oxidation.

A temperature programmed desorption study of non-thermal plasma modified γ-Al2O3

In this paper, the effect of non-thermal RF plasma modification on the point of zero charge (PZC) of γ-Al2O3 has been explored. Samples of alumina were first modified with air, CO2, N2 or Ar plasma and then measurements of the PZC were taken. In order to determine the mechanism behind PZC shift, the surface area and crystal phase were measured for each sample using nitrogen physisorption (BET) and X-ray diffraction (XRD). Additionally, the presence of plasma gas on the surface of alumina was determined qualitatively using a modified temperature programmed desorption (TPD) technique. Air and CO2 modification of alumina powder decreased the PZC from 7.48 to 4.86 and 6.57 respectively. However, N2 and Ar modification did not result in any PZC shift. BET and XRD measurements showed no significant surface area or phase changes occurred due to non-thermal plasma modification. TPD profiles for air and CO2 modified samples showed new peaks corresponding to the adsorption of plasma ions on the alumina surface. These results demonstrate that PZC changes in a support after plasma treatment is caused by the adsorption of plasma species.

Fe/MCSAC catalysts surface modified with nitrogen DBD non‐thermal plasma for carbonyl sulfide catalytic hydrolysis activity enhancement

The removal of carbonyl sulfide (COS or S=C=O) from gas streams over Fe/microwave coconut‐shell activated carbon (MCSAC) catalysts modified by dielectric barrier discharge non‐thermal plasma (NTP) were investigated. The properties of Fe/MCSAC catalysts modified by NTP in different conditions, included kinds of reactors, treatment times and input voltages. The surface properties were evaluated by means of energy‐dispersive X‐ray spectrometry, Brunauer Emmett Teller, X‐ray photoelectron spectroscopy methods and theoretical calculation, which could help us understand the effects of the plasma treatment. The experiments results showed that the COS hydrolysis activities of Fe/MCSAC catalysts were largely enhanced after NTP modification. And the optimal reactor type, treatment time and input voltage were plate‐plate type, 10 min and 35 V, respectively. The catalytic activity enhanced effectually due to the improvement of active component's dispersion after NTP modification. In addition, the extended oxygen functional groups on NTP‐modified catalyst's surface could contribute to a higher activity for COS catalytic hydrolysis at low temperature. The investigation results indicate that non‐thermal plasma treatment is an effective way to manipulate catalyst surface properties for COS catalytic hydrolysis reaction. Copyright © 2017 John Wiley & Sons, Ltd.

Low Temperature Catalytic Hydrolysis of Carbon Disulfide on Activated Carbon Fibers Modified by Non-thermal Plasma

In order to improve the carbon disulfide (CS2) catalytic hydrolysis efficiency of activated carbon fibers (ACFs), ACFs surface was modified by non-thermal plasma (NTP). In particular, the effects of modification conditions on the catalyst properties were studied, including the reactor structure, modification atmosphere, modification time, output voltage and discharge gap. The catalytic activity study showed that ACFs with NTP modification enhanced CS2 catalytic hydrolysis. The optimal reactor structure, modification atmosphere, modification time, output voltage and discharge gap was a coaxial cylinder, an N2 atmosphere, 5 min, 7 kV and 7.5 mm, respectively. The effect of the NTP modification on the micro-structural properties of the ACFs was characterized using scanning electron microscopy (SEM), Brunauer–Emmett–Teller (BET) and X-ray photoelectron spectroscopy (XPS) methods. The results showed that NTP modification improved the dispersion of functional groups and increased the number of oxygen-containing and nitrogen-containing functional groups, thus the catalytic activity could be enhanced. The present results indicated that NTP modification was an effective way to manipulate ACFs surface properties for the CS2 catalytic hydrolysis reaction.

Surface modification of Fe/MCSAC catalysts with coaxial cylinder dielectric barrier discharge plasma for low-temperature catalytic hydrolysis of CS2

The removal performances of carbon disulphide (CS2) from gas streams over microwave coconut shell activated carbon (MCSAC) supported Fe (Fe/MCSAC) modified by a dielectric barrier discharge (DBD) non-thermal plasma (NTP) were investigated. The properties of Fe/MCSAC catalysts modified by NTP in different conditions, including the reactor structures, modification atmospheres, input voltages, treatment times and discharge intervals, were also studied. A study of the catalytic activities showed that Fe/MCSAC catalysts with NTP modification better catalytically hydrolyse CS2, and the optimal reactor type, modification atmosphere, input voltage and treatment time were a coaxial cylinder, an NH3 atmosphere, 20V, 10min and 2mm, respectively. Temperature programmed desorption of CO (CO-TPD), X-ray photoelectron spectroscopy (XPS), Brunauer Emmett Teller (BET), theoretical calculation and Fourier transform infrared spectrum (FT-IR) analysis methods, which were designed to understand the effect of the plasma treatment and the hydrolysis mechanism of CS2. The catalytic activity could be enhanced effectively by improving the dispersion of the active components and increasing the number of oxygen-containing groups and potassium-containing groups after NTP modification. The investigation indicated that NTP treatment is an effective way to manipulate the catalyst surface properties for the CS2 catalytic hydrolysis reaction.

Adsorptive removal of gas-phase mercury by oxygen non-thermal plasma modified activated carbon

The effects of oxygen non-thermal plasma modification on the surface properties and mercury removal performance of activate carbon (AC) were investigated. The raw and modified ACs were characterized by N2 adsorption/desorption, scanning electron microscope (SEM), Boehm titration and Fourier Transform Infrared Spectrometer (FTIR). The results showed that the surface textual properties of the modified ACs were slightly damaged, but the surface chemistries such as the content of surface oxygen-containing groups were significantly changed. The elemental mercury removal performance of raw and modified ACs were also evaluated in a quartz tube fix-bed reactor under N2 atmosphere. The results indicated that the AC treated with oxygen non-thermal plasma had better elemental mercury removal performance compared to the raw AC. This reason was attributed to the oxygen non-thermal plasma treatment increasing the ester groups (CO), carbonyl groups (CO) and adsorption activate sites on AC surface, which played an important role in the adsorption of elemental mercury. The adsorption kinetic of raw and modified ACs could be best described by the Pseudo-first-order model and Pseudo-second-order model, which implied that external diffusion and chemisorption were the control step in the mercury adsorption process of raw and modified ACs.

Low-temperature hydrolysis of carbon disulfide using the Fe[sbnd]Cu/AC catalyst modified by non-thermal plasma

The removal of carbon disulfide (CS2) from gas streams via FeCu/AC catalyst modified by non-thermal plasma (NTP) were investigated. In particular, effects of treatment conditions on the catalyst’s properties were studied. The properties change in the catalyst after NTP modification is measured by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and scanning electron microscope (SEM). The results showed relatively high capacities of FeCu/AC catalyst modified by NTP for removal of COS. The catalytic activity and sulfur capacity of material enhanced due to the extended oxygen functional groups on the surface of carbons. In addition, the surface area and micro-pore volume on NTP-modified catalysts played another important role in the process of CS2 removal.

MnOx Catalysts Modified By Nonthermal Plasma For NO Catalytic Oxidation

Nonthermal plasma modification (NTPM) has been applied to MnOx catalysts for the catalytic oxidation of nitrogen oxide (NO) at low temperature (50–250 °C), and much higher NO conversion was obtained over the nonthermal plasma-treated catalysts. These modified catalysts were characterized in different ways—scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Brunauer–Emmett–Teller (BET), and Fourier transform infrared (FT-IR)—and the results can help us to understand the effect of the plasma treatment. The results showed that the surface active sites of these catalysts were enhanced with the treatment of plasma, which improved the dispersion of catalysts. In addition, after NTPM, a considerable amount of deposition with limited depths appeared on the MnOx surface, the average pore size was slightly enlarged, and the pore size distributions of the MnOx became wider. Also, XPS results revealed that the NTPM could increase the oxygen, nitrogen, and kalium functi...