Photo-assisted Reaction Research Articles

C3N4/Se-CNTs as Advanced Metal-Free Catalysts for the Photoassisted Electrocatalytic Oxygen Evolution Reaction.

Photoassisted electrocatalysis is a frontier direction of electrocatalysis for promoting energy conversion. In this work, a metal-free C3N4/Se-CNTs is reported as a novel catalyst for photoassisted electrocatalytic oxygen evolution reaction (OER). C3N4 has an appropriate bandgap, high specific surface area, and long-term stability. CNTs can modulate the electronic environment of C3N4 by strong π-π interaction and greatly enhance the separation efficiency of photogenerated carriers. The distributed Se nanoparticles in CNTs can further increase the charge transfer ability. As a metal-free catalyst, the C3N4/Se-CNTs exhibits an overpotential of 231 mV at a current density of 10 mA cm-2 and a small Tafel slope of 52 mV dec-1 under illumination, which ranks among the best catalysts for photoassisted OER performance, surpassing most noble and transition metal-based catalysts. The result demonstrates the great potential of C3N4-based catalysts in the photoassisted OER process and provides a new perspective to explore the excellent metal-free OER catalysts.

Boosting charge separation and active sites exposure by hollow S-scheme MoSe2/Fe2O3 heterojunction for enhanced photocatalytic peroxymonosulfate activation towards ciprofloxacin removal

Regulating the properties of heterogeneous catalyst for efficient peroxymonosulfate (PMS) activation to pollutants degradation remains a challenge in photo-assisted Fenton-like reaction (PF) system. In this study, the novel S-scheme MoSe2/Fe2O3 (H-FMS) heterojunction with hollow nanostructure was successfully developed as visible-light-driven PMS activator for removal of ciprofloxacin (CIP). The prepared H-FMS catalyst in PMS/H-FMS/light system exhibits outstanding photocatalytic performance for CIP degradation, achieving 95.92 % removal of 5 mg/L CIP in 30 min with 0.5 mM PMS. The construction of S-scheme heterojunction provides photoinduced carriers with longer lifetime and higher redox abilities, thus sufficient photogenerated carriers are supplied to directly activate PMS. Simultaneously, the hollow nanostructure possessing multiple light reflection and scattering behaviors further facilitates the utilization of visible light. More importantly, high concentration of photoinduced electrons with high reduction ability in MoSe2 is conducive to continuous exposure of Mo4+ active sites for PMS activation through cycling between transition metal valence states. Overall, effectively separated electron-hole pairs and continuously exposed transition metal active sites both contribute to efficient activation of PMS as well as multi-path generation of ROS, leading to significant improvement in CIP degradation. The results of quenching experiment, electron spin resonance (ESR) technology, liquid chromatography-mass spectrometry (LC-MS) and density functional theory (DFT) calculation confirm that both free radicals (SO4∙-, •OH and O2∙-) and non radicals (1O2 and h+) attack the active sites of CIP possessing high Fukui index, thus contributing to CIP degradation. This work would provide a novel insight for future development and application of photocatalytic PMS activation catalysts in water remediation.

In Situ Construction of SnS2@SnO2 Heterostructure for Photo-Assisted Electrocatalysis of Oxygen Evolution Reaction.

Photo-assisted electrocatalysis has arisen as a promising approach for hydrogen generation by incorporating photocatalysts into electrocatalysts. 2D SnS2 is a photocatalyst that absorbs visible light. However, the rapid recombination of photo-generated electron-hole pairs significantly reduces the overall photocatalytic efficiency of SnS2, limiting its practical application. Thus, this study prepares an in situ heterojunction SnS2@SnO2 using a one-step hydrothermal method. The degradation efficiency of methyl orange (MO) using SnS2@SnO2 is measured, achieving a degradation rate of 92.75% within 1h, which is 1.9 times higher than that of pure SnS2. Additionally, FeNiS/SnS2@SnO2 is synthesized and exhibited significant improvements in the photo-assisted oxygen evolution reaction (OER). It achieves an overpotential of 260mV and a Tafel slope of 65.1mVdec-1 at 10mAcm-2, showing reductions of 11.8% and 31.8%, respectively, compared to FeNiS alone. These enhancements highlight the strong photo-response capability of SnS2@SnO2. Under the internal electric field of SnS2@SnO2, the photogenerated electrons in the conduction band of SnS2 quickly move toward SnO2, facilitating efficient photocatalytic reactions. FeNiS, with a lower Fermi energy level (EF), facilitates electron transfer from SnS2@SnO2 and enhances OER performance by efficiently participating in the reaction. This study paves a new path for 2D photocatalyst materials.

BioTemplated Fe3+-Doped g-C3N4 Heterojunction Micromotors for the Degradation of Tetracycline through the Photo-Fenton Reaction

The excessive discharge of antibiotics into aquatic systems is a major issue in many countries worldwide and poses a threat to human health and the sustainable development of society. Hence, developing efficient treatment methods and purification technologies to degrade antibiotics is essential. Herein, we present the synthesis of low-cost, self-propelled tubular Fe3+-incorporated graphitic carbon nitride (g-C3N4-Fe@KF) micromotors using kapok fibers (KFs) as templates and their application as photo-catalysts for the photo-Fenton degradation of tetracycline (TC) under visible-light irradiation. The g-C3N4-Fe@KF micromotors moved rapidly when being propelled by oxygen bubbles generated in a hydrogen peroxide (H2O2) solution as a result of a photo-assisted Fenton reaction. The motion behavior of the g-C3N4-Fe@KF micromotors was dependent on the concentration of H2O2 and the length of the micromotors. The propulsion mechanism was discussed in detail. The micromotors efficiently degraded antibiotics via the photo-Fenton process. Photo-Fenton degradation efficiency was attributed to the synergistic effects of the doped Fe3+ and g-C3N4 under visible-light irradiation and self-propulsion of the micromotors. In addition, the micromotors possessed good reusability, thereby efficiently realizing multiple cycles of degradation. The current work offers an avenue for the design of micromotors, using inexpensive approaches, for various potential environmental applications.

Key role of carbon as an efficient electron bridge in CuO@C@Fe2O3 for enhancing H2O2 activation during photo-assisted Fenton-like reaction

The Fe3+/Fe2+ cycle has been identified as the rate-limiting step in the Fenton system, and many efforts have been made to promote the Fe3+ reduction via external electrons provided by various electron donors. However, how to design an efficient electron transport pathway and then inhibit the invalid electron shuttle has been largely underestimated. In this study, two kinds of heterogeneous Fenton catalysts of CuO@Fe2O3 and CuO@C@Fe2O3 were prepared. The key role of carbon in transporting electrons as an electron bridge and its enhancement mechanism in photo-assisted Fenton-like performances were explored in detail. Compared with CuO@Fe2O3, the removal efficiency of tetracycline (TC) and the corresponding pseudo-first order reaction rate constants over CuO@C@Fe2O3 increased significantly from 88.6 % and 0.1054 min−1 to 99.7 % and 0.2058 min−1, respectively. Based on a series of probe experiments, visible light irradiation can promote the reduction of Cu2+ to Cu+, then the carbon in CuO@C@Fe2O3 can effectively transfer electrons from Cu+ to Fe3+, enhancing the Fe3+/Fe2+ cycle and the following Fenton-like efficiency. Since more ·OH while less ∙O2- was produced over CuO@C@Fe2O3, which further supports the fact that the enhanced Fe3+/Fe2+ cycle was due to the transfer electron from Cu+ to Fe3+ instead of the Haber-Wiss mechanism. Hence, this study provides new insight for effectively improving the transfer efficiency and effective utilization of electrons in Fenton systems.

Suppression of hydrogen evolution reaction in CO2 reduction by functionalizing Ag-decorated Si electrode with phthalocyanine

The photo-assisted electrochemical CO2 reduction reaction (CO2RR) toward CO stands as a highly promising pathway for addressing environmental challenges and produces valuable chemicals. In this study, a novel pl-Si/Ag/Pc electrode was developed with the surface enveloped by an amorphous phthalocyanine overlayer. The pl-Si/Ag/Pc electrode has gained recognition as a catalyst of exceptional quality, displaying superior activity, selectivity toward CO, and stability. A synergistic mechanism has been revealed from experimental results that Ag served as active centers for CO2RR, Pc facilitated CO2 adsorption and suppressed the competing HER reaction. Functionalizing the surface of electrode with Pc enhanced the CO selectivity (FECO at 90.8 % under −1.5 V vs RHE) during the CO2RR process and reduced the cost in following product separation procedures. This study presents an uncomplicated yet effective approach for formulating durable and discerning electrocatalysts dedicated to the utilization of CO2.

Electrochemical reconstitution of Prussian blue analogue for coupling furfural electro-oxidation with photo-assisted hydrogen evolution reaction

Prussian blue (PB) and its analogues (PBAs) have served as effective electrocatalysts for the oxidation of biomass. However, the PBA-based catalyst is prone to structural changes in the electrochemical process under alkaline medium, which may alter the mechanism and kinetics of the electrocatalytic reaction. Herein, a PBA-based catalytic electrode (NiFe/Ni) is obtained by depositing Ni2[Fe(CN)6] on Ni foam through a wet chemistry method. It is found that Ni2[Fe(CN)6] converts to high-valence NiOOH during the electrochemical process in alkaline medium. Meanwhile, the polarons generated by lattice deformation in Ni2[Fe(CN)6] can transform into NiOOH with oxygen vacancies (v-NiOOH). The obtained v-NiOOH endows the catalytic electrode with superior performance for the electro-oxidation of furfural compounds to furoic acids. The in-situ ATR-FTIR and furfural temperature-programmed desorption further prove that the fast furfural electro-oxidation kinetics can be ascribed to the high-flux furfural adsorption ability of the v-NiOOH. In addition, the electrocatalytic oxidation of furfural and photo-assisted hydrogen evolution reaction are integrated into a water-splitting electrolyzer. Compared with the conventional water-splitting electrolyzer, the integrated electrolyzer can reduce the cell voltage by 480 mV at 100 mA cm−2. This work proves the electrochemical reconstitution of the PBA-based catalysts for biomass oxidation under alkaline electrolyte, which provides a new way for the design of PBA-based electrocatalysts.

Bimetallic (Cu, Zn) ZIF-derived S-scheme heterojunction for efficient remediation of aqueous pollutants in visible light/peroxymonosulfate system

The design of suitable catalyst is the bottleneck in the photo-assisted Fenton-like reaction system. Here we constructed a S-scheme heterojunction consisted of CuO and Cu doped ZnO using Cu-ZIF-8 as precursor. The as-prepared composite catalyst possesses outstanding catalytic activation performance and broad-spectrum degradation capacity. To clearly fit and describe the overall reaction, a pseudo-third-order kinetic model was developed based on the second-order peroxymonosulfate (PMS) consumption and first-order methylene blue removal. The catalyst/visible light/ PMS composite reaction system provides remarkable mineralization and anti-interference ability, and is environmental friendliness. The interaction of Cu/Zn bimetallic sites realized the effective utilization of PMS, accelerated the PMS activation and promoted the formation of the highly oxidative SO5•−. Overall, this work provides new systematic insights on PMS activation by Cu/Zn bimetallic oxide S-scheme heterojunction and is of significance for sewage purification.

The synergy of Ni doping and oxygen vacancies over CeO2 in visible light-assisted thermal catalytic methanation reaction

The photo-assisted thermal catalytic system has provided a new alternative way to drive highly efficient CO2 methanation reaction. In this work, we investigated the role of visible light for thermal catalytic methane synthesis, emphasizing the synergy effect of Ni doping and oxygen vacancies for the hydrogenation of CO2 over Ni-CeO2 catalysts. It was found that the optimal 7.5 wt% Ni-CeO2 catalysts exhibited the best visible light-promoted CO2 methanation performance. At 250 °C, the light-promoted performance increased from 0.67 to 0.93 mmol−1·g−1·h which increased by 39 %. Extensive characterization demonstrates that heteroatom Ni doping increases the content of oxygen vacancies which narrows the band gap and improves the electron density of the catalyst, resulting in accelerating the transformation of carbonate and CO intermediate species which is beneficial to yield CH4. Furthermore, the visible-light-induced regeneration of oxygen vacancies also provides more active site to facilitate the adsorption and activation of CO2 which co-promoted the photo-assisted thermal catalytic CO2 methanation reaction. The synergy effect of Ni doping and oxygen vacancies provide a new strategy to design a high-efficiency photo-assisted thermal catalyst.

Efficient photo-assisted Fenton-like reaction of yolk-shell CuSe(Cu2Se)/g-C3N4 heterojunctions for methylene blue degradation.

Herein, a CuSe(Cu2Se) yolk-shell structure (CC) was synthesized when room temperature was 25 degree Celsius using Cu2O as a soft template, and the g-C3N4/CuSe(Cu2Se) heterojunction (CC-G) was formed by coupling appropriate amounts of g-C3N4 in the selenization process to provide a novel, green, economical, and efficient photo-Fenton catalytic material. Photo-Fenton degradation experiments proved that in the presence of hydrogen peroxide (H2O2), a small amount of g-C3N4 hybridization on Cu-based Fenton catalysts significantly improved methylene blue (MB) degradation. The suitable amount of g-C3N4 hybridization was selected according to the degradation efficiency. The mass of g-C3N4 constituted 20% of the mass of the Cu2O soft template. The composite material prepared using this combination (CC-G-20) exhibited the best MB degradation performance. The MB degradation efficiency in the CC-G-20/H2O2/visible light system was almost 98.3% after 60 min, which is higher than those of the parent materials (g-C3N4, 12.7%; CC, 58.6%) and had cyclic stability. The catalytic system can also stably degrade MB under dark conditions, where the MB degradation was almost 82% after 60 min. The heterojunction prevented excessive electrons and holes (e - and h+) recombination, stabilizing the reactive active substance of hydroxyl in the photo-Fenton-like catalytic system. Electron paramagnetic resonance and photoluminescence experiments confirmed this inference.

Boosting photo-assisted efficient electrochemical CO2 reduction reaction on transition metal single-atom catalysts supported on the C6N6 nanosheet.

CO2 reduction to value-added chemicals turns out to be a promising and efficient approach to resolve the increasing energy crisis and global warming. However, the catalytic efficiency of CO2 reduction reaction (CO2RR) to form C1 products (CO, HCOOH, CH3OH, CH4) needs to be quite efficient. Herein with the help of density functional theory, CO2RR towards C1 products was investigated on a transition metal (TM = Fe, Co, Ni) embedded C6N6 framework. The stable geometry of the catalysts, CO2 adsorption configurations, and CO2RR mechanisms were systematically studied for all the systems considered. The possible different adsorption configurations and adsorption energy calculations indicated that CO2 could be chemically adsorbed on the Co@C6N6 system. On the other hand, physical adsorption of CO2 is more preferable on Fe@C6N6 and Ni@C6N6 systems. As a competitive reaction, hydrogen evolution reaction (HER) was investigated and the systems were found to show more selectivity for CO2RR than for HER. OCHO formation turned out to be more favorable than COOH formation as initial protonation intermediates for CO2RR on the TM@C6N6 systems. The present work demonstrates that the Co@C6N6 catalyst can favor the electrocatalytic CO2RR among all systems. In addition, the photocatalytic activity of the systems was also investigated. The systems are found to be active for photoreduction of CO2 to CH3OH and CH4 in the presence of reducing agents such as H2 and H2O as they possess appropriate absorption spectrum in the visible region as well as suitable band edge positions. These findings open a way for designing single atom catalysts for important catalytic reactions.

Near‐infrared light-assisted methanol oxidation reaction over the ferrous phosphide

Ferrous phosphide (Fe2P) possesses both functions of near‐infrared light (NIR) responsive and metal-support interactional behaviors, which will show great significance in photo-assisted electrocatalytic methanol oxidation reaction (MOR) areas. Hereby, we use Fe2P as the support to load Pt nanoparticles and investigate the performance of the as-obtained Pt-Fe2P for MOR. The results show that the synergistic effect of photocatalysis and electrocatalysis contributes to the high-performance MOR, especially under NIR irradiation. The as-obtained Pt-Fe2P also shows excellent photoelectric response performance and long-time stability of photo-electrocatalytic activity with the assistance of NIR illumination. The mass activities of the Pt-Fe2P catalysts with the assistance of NIR towards MOR is 2430.0 mA mg−1Pt, 4.7 times superior to the dark condition (521.1 mA mg−1Pt), which is obviously better than that of traditional electrocatalysts and some reported photo-electrocatalysts. The strong metal-support interaction between Pt and Fe2P together with NIR excited hot electrons from Fe2P result in the above superior photo-electrocatalytic methanol oxidation abilities. The present investigation offers a NIR-assisted electrocatalytic MOR strategy, which may be a feasible approach to further elevate the catalytic performance for MOR in photo-assisted direct methanol fuel cells (DMFCs).

NiCo2O4/BiOCl/Bi24O31Br10 ternary Z-scheme heterojunction enhance peroxymonosulfate activation under visible light: Catalyst synthesis and reaction mechanism

The Z-scheme heterostructure for photocatalyst can effectively prolong the lifetime of photogenerated carriers and retain a higher conduction/valence band position, promoting the synergistic coupling of photocatalysis and peroxymonosulfate (PMS) activation. In order to fully utilize the luminous energy and realize the efficient activation of PMS, this work achieved successful construction of NiCo2O4/BiOCl/Bi24O31Br10 ternary Z-scheme heterojunction by simultaneously synthesizing BiOCl and NiCo2O4 with NiCl2 and CoCl2 as the precursors. The intercalated BiOCl could serve as a carrier migration ladder to further achieve the spatial separation of electron-hole pairs, so that the oxidation and reduction processes separately occurred in different regions. Compared with the reported catalysts, the as-prepared composites exhibited the enhanced removal efficiency for tetracycline hydrochloride (TCH) in the visible light/PMS system, with a degradation efficiency of 85.30% in 2 min, and possessed good stability. Z-scheme heterojunction was shown to be beneficial for maximizing the superiority of photo-assisted Fenton-like reaction system. The experimental and characterization results confirmed that both non-radicals (1O2) and radicals (SO5•− and SO4•−) were involved in the reaction process and the SO5•− generated by the oxidation of PMS played a crucial role in the TCH degradation. The possible reaction mechanism was finally proposed. This study provided new insight into the Z-scheme heterostructure to promote the photo-assisted Fenton-like reaction.

Few-layered black phosphorus/cucurbit[6]uril as a Pd catalyst support for photo-assisted electrocatalytic ethanol oxidation reaction

In this work, macrocyclic molecule cucurbit[6]uril (CB[6])-modified two-dimensional black phosphorus nanosheets (BPNSs) used as photoactivated support were synthesized by a simple solvothermal method. Palladium nanoparticles were anchored on the surface of BP-CB[6] to obtain the composite material Pd/BP-CB[6] by using a chemical reduction method. Then, the electrocatalytic activity of the composite material modified electrode in the ethanol oxidation reaction (EOR) was investigated. The Pd/BP-CB[6] catalyst exhibits a high mass activity (1420 mA·mgPd−1), which is 4.1 times higher than commercial Pd/C. Impressively, the ethanol oxidation activity of the Pd/BP-CB[6] electrode under visible light irradiation (1900 mA·mgPd−1) is 1.34 times higher than under dark conditions. The result is obtained through a series of evaluations, including cyclic voltammetry, chronopotentiometry, chronoamperometry, and electrochemical impedance spectroscopy, in which the prepared Pd/BP-CB[6] shows higher catalytic activity and stability than Pd/BP. These results suggest that the synergistic effect of photocatalysis and electrocatalysis improves the electron transport kinetics of the Pd/BP-CB[6] electrode in the EOR process. Two-dimensional black phosphorus nanosheets can be used as promising photoactivated supports, to which functional material CB[6] is fixed by hydrogen bonding. Meanwhile, the electrostatic interaction between CB[6] and noble metal helps to improve the stability of the catalyst. This work provides a new idea for developing efficient photoresponsive electrode material in direct ethanol fuel cells.

Novel Ternary CuO–CeO2/g-C3N4 Heterogeneous Catalyst for Removing Methyl Orange Dye via Photo-Assisted Fenton-like Reaction

Novel Ternary CuO–CeO2/g-C3N4 Heterogeneous Catalyst for Removing Methyl Orange Dye via Photo-Assisted Fenton-like Reaction

Cu(ii)-vitamin C-complex catalyzed photo-induced homocoupling reaction of aryl boronic acid in base-free and visible light conditions.

In this work, the photocatalytic efficiency of Cu(ii)–vitamin C complex immobilized on titanium dioxide nanoparticles was exploited in the photo-assisted homocoupling reaction of aryl boronic acids under heterogeneous conditions. The homocoupling reaction affords the corresponding symmetrical biaryls in 50–97% yields at ambient temperature in the air under visible light irradiation without any need for any additive such as base or oxidant. This method tolerates various substituents on the aryl boronic acids such as halogen, carbonyl, and a nitro group. The light-dependent photocatalytic performance of the title catalyst evaluated by action spectra revealed a maximum apparent quantum efficiency (AQYs) at 410 nm demonstrating the visible-light-driven photocatalytic reaction. The as-prepared nano biophotocatalyst proved to be reusable at least six times without losing its activity. Thus this work exhibits a favorable method from the environmental and economic point of view which enables the industrially important reactions such as coupling reactions, to be carried out efficiently under photocatalytic and practically attainable conditions.

Visible light-assisted organocatalytic α-acyloxylation of ketones using carboxylic acids and N-halosuccinimides.

The α-acyloxylcarbonyl motif can be found in many important pharmaceuticals and biologically active natural products and their derivatives. In this manuscript, the direct synthesis of α-acyloxylketones from ketones and readily available carboxylic acids was realized using a photo-assisted halogen bond-mediated organocatalytic α-acyloxylation reaction. The desired α-acyloxylation products were obtained in good to high yields.

Self-powered electrochemical sensing platform based on zinc-air battery via synergy of the light filtering effect and photoassisted oxygen reduction reaction

Self-powered electrochemical sensor has received widespread attention due to it does not require an external power supply. In this study, a self-powered electrochemical sensor based on visible light assisted zinc-air battery (SPES-ZAB) was used as a feasible platform to identify changes in light intensity, which was developed a concealed sensing strategy to expand the application range of UV-Vis absorption spectroscopy. Typically, the core of the zinc air battery is an oxygen reduction catalyst, of which the realization of the oxygen reduction reaction through photo-assisted catalyst is one of the emerging strategies. In this self-powered system, zinc as anode and the polyterthiophene as photocathode were used to construct zinc-air battery and realize the output voltage of the SPES-ZAB through the regulation of light intensity. In addition, we used rhodamine B, potassium permanganate and dopamine self-oxidation solution as model analyte to study the light filtering effect and the sensing performance of SPES-ZAB. Through the filtering effect of the solution on the light intensity, the photocathode oxygen reduction process can be adjusted to achieve the ability of the SPES-ZAB to detect the target. Compared to the results of UV-Vis absorption spectroscopy, the SPES-ZAB exhibits good linear relationship range and excellent universality in the detection of high-concentration colored solutions. This is the first time the use of SPES-ZAB as sensing platform to detect the target in homogeneous system, which will expand the application range of self-powered sensors.

Hybrid Structure of a ZnO Nanowire Array on a PVDF Nanofiber Membrane/Nylon Mesh for use in Smart Filters: Photoconductive PM Filters

A nanofiber membrane with a high surface-to-volume ratio has advantages in applications such as those used for particulate matter filtration and gas detection. To maximize the potentials of the membrane structure, recent research has been attempted to control nanofiber geometries. In this paper, surface modification of a nanofiber membrane with a metal/ceramic nanostructure is performed to improve multi-functional filter performance, enhancing fine particle filtration and toxic gas absorption. Here, a smart filter is fabricated by electrospinning polyvinylidene difluoride (PVDF) nanofiber onto a nylon mesh and hydrothermal synthesis of ZnO nanoparticles onto a nanowire array on a PVDF nanofiber surface. On the ZnO nanowires–PVDF nanofiber layer filter, the pressure difference (ΔP = 4.13 kPa) is higher than the pure PVDF nanofiber layer. However, the filtration efficiency is 94.3% for a 0.3 μm particle size, which is higher than that of other sizes. Additionally, a ZnO nanowire array with high density on a PVDF nanofiber layer affects sensitivity (S = 39.37), with high resolution. The photocurrent characteristics of a smart filter have the potential for a photo-assisted redox reaction to detect toxic polar molecules in continuous airflow in real-time in indoor environments.

Wet etching for isolation of N-polar GaN HEMT structure by electrodeless photo-assisted electrochemical reaction

Electrodeless photo-assisted electrochemical etching was performed in an N-polar GaN high-electron-mobility transistor to obtain device isolation with a flat wet etching surface. The root mean square roughness of the surface after 30 nm etching was 3.4 nm, and a relatively flat etched surface was confirmed. The resistance between the electrodes changed from around 102 Ω to approximately 108 Ω by 30 nm etching.