Mesoporous Layer Research Articles

Crystal-Size-Induced Band Gap Tuning in Perovskite Films.

A comprehensive picture explaining the effect of the crystal size in metal halide perovskite films on their opto‐electronic characteristics is currently lacking. We report that perovskite nanocrystallites exhibit a wider band gap due to concurrent quantum confinement and size dependent structural effects, with the latter being remarkably distinct and attributed to the perturbation from the surface of the nanocrystallites affecting the structure of their core. This phenomenon might assist in the photo‐induced charge separation within the perovskite in devices employing mesoporous layers as they restrict the size of nanocrystallites present in them. We demonstrate that the crystal size effect is widely applicable as it is ubiquitous in different compositions and deposition methods employed in the fabrication of state‐of‐the‐art perovskite solar cells. This effect is a convenient and effective way to tune the band gap of perovskites.

Crystal‐Size‐Induced Band Gap Tuning in Perovskite Films

AbstractA comprehensive picture explaining the effect of the crystal size in metal halide perovskite films on their opto‐electronic characteristics is currently lacking. We report that perovskite nanocrystallites exhibit a wider band gap due to concurrent quantum confinement and size dependent structural effects, with the latter being remarkably distinct and attributed to the perturbation from the surface of the nanocrystallites affecting the structure of their core. This phenomenon might assist in the photo‐induced charge separation within the perovskite in devices employing mesoporous layers as they restrict the size of nanocrystallites present in them. We demonstrate that the crystal size effect is widely applicable as it is ubiquitous in different compositions and deposition methods employed in the fabrication of state‐of‐the‐art perovskite solar cells. This effect is a convenient and effective way to tune the band gap of perovskites.

One‐Step Synthesis of Carbon‐Protected Co3O4 Nanoparticles toward Long‐Term Water Oxidation in Acidic Media

The design and development of highly efficient and stable oxygen evolution reaction (OER) electrocatalysts in acid media are important for various renewable technologies. Herein, an advanced Co3O4 electrocatalyst supported on a mesoporous hydrophobic carbon paper (Co/29BC) is formed via a simple one‐step thermal decomposition of cobalt nitrate. Through this novel approach, the amorphous carbon layer resulting from the thermal decomposition of carbon‐containing species in the mesoporous layer provides enhanced electronic conduction and protection against corrosion to the Co3O4 nanoparticles. Equally important, the OER performance is found to be correlated with the morphology and surface composition of Co3O4. With optimized Co3+ active sites and oxygen vacancies at the metal oxide surface, the Co3O4 catalyst shows superior OER performance and durability in a proton exchange membrane (PEM) water electrolyzer, with a small overpotential (350 mV) at a constant current density of 10 mA cm−1 for over 50 h. Accordingly, this work provides new insights toward the design of high‐performance and highly stable OER electrocatalysts in corrosive acidic environments.

Modification of TiO2 and NiO charge selective mesoporous layers using excessive Y and Li additions for carbon based perovskite solar cells

Carbon based perovskite solar cells are rapidly emerging as promising photovoltaic devices, combining low cost production and prolonged device operation, due to the exclusion of polymeric conductors and integration of highly durable metal oxide charge selective layers. Modification of metal oxide mesoporous layers via element additions and enhancement of electrical conductivity is a major strategy for reduced internal resistances inside the cell. This work investigates the effect of excessive Y and Li additions on the charge selective mesoporous layers. A novel flame synthesis method can be successfully employed for production of yttrium added TiO2 (Y:TiO2) and conductive lithium added NiO (Li:NiO) nanoparticles. This novel methanol combustion method is an effective strategy for incorporation of additives into host lattices, resulting in modified mesoporous layers. Ultraviolet photoelectron spectroscopy studies reveal a profound effect of Li and Y additions on the electronic band structure of the particles. Electrochemical impedance studies confirms that modification of TiO2 with excessive yttrium atoms results in suppressed charge injection, where excessive lithium addition enhances the charge transport properties of the NiO layer. Power conversion efficiency of the pristine NiO based cells are enhanced from 8.38% to 9.63% upon lithium addition, in a TiO2/MgO/Li:NiO/carbon configuration.

Synthesized TiO2 Mesoporous by Addition of Acetylacetone and Graphene for Dye Sensitized Solar Cells

This study mixed acetylacetone (Acac, 1, 2, and 3 mL) and graphene powder (GP, 0 wt.%, 0.001 wt.%, 0.003 wt.% and 0.005 wt.%) with TiO2 mesoporous (TiO2 powders: 20 g and particle size ~30 nm) to enhance the optoelectronic performances of dye sensitized solar cells (DSSC). Sponge-like structure TiO2 mesoporous layers is a requirement for obtaining high efficiency DSSC, which ia synthesized by spin-coating techniques. The dense TiO2 blocking layer (using peroxo-titanium complex) has a uniform, dense structure and completely adheres to the substrates to avoid charge recombination. The X-ray diffraction (XRD) and transmission electron microscopy (TEM) analyses of the TiO2 films display the anatase type phase with preferred orientation along the (101) direction. After being ball milled, the TiO2 mesoporous particle size almost remains unchanged. For mixing the Acac with TiO2, the Raman intensity relatively increased, and the band gap energy (Eg) value decreased from 3.223 eV (for pure TiO2) to 3.076 eV (for 2 mL Acac). Raman spectroscopy is used to evaluate the GP elements. It can be seen the intensity ratio (ID/IG) and (I2D/IG) was enhanced when the GP concentration increased. Using mixed Acac 2 mL and GP 0.003 wt.% with a TiO2 mesoporous, led to increases in the open circuit voltage (VOC), short circuit current density (JSC) and fill factor (FF). If a fluorine-doped tin oxide is used instead of an indium tin oxide glass substrate, the photovoltaic efficiency of DSSC increases from 5.45% to 7.24%.

Ammonia-vapour-induced two-layer transformation of mesoporous silica coatings on various substrates

We prepared mesoporous silica layers by sol-gel dip-coating technique on various substrates (silicon, polycarbonate, microscope glass and quartz) with the aid of a pore-forming triblock copolymer (Pluronic PE10500). The freshly deposited layers were aged in an aqueous ammonia solution atmosphere. Two types of thermal curing were implemented depending on the substrates: a low-temperature heat treatment at 120 °C for 13 hours or a high-temperature heat treatment at 480 °C for 1 hour. We carried out the porogen extraction of the copolymer molecules from the low-temperature heat-treated samples in a water washing step.Optical spectroscopy measurements gave evidence of a significantly improved and long-lasting light transmission of coatings. The maximum light transmission was 98.3% on glass and 97.6% on polycarbonate after 4 years of storage. TEM investigations showed thin layers with distorted face centred cubic structure.Spectroscopic ellipsometry and ellipsometric porosimetry studies showed a “two-layer” structure. The applied synthesis technique promoted the formation of a double layer structure with relatively thick (10–25 nm) pore sizes. The pseudomorphic transformation rearranged the silica/copolymer structure in presence of ammonia. The transformation was incomplete and resulted in a low porosity (23–34%) upper-layer and a high porosity (40–76%) lower-layer.

Bifunctional SnO2 Colloid Offers No Annealing Effect Compact Layer and Mesoporous Scaffold for Efficient Perovskite Solar Cells

AbstractSnO2 compact layer (c‐SnO2) frequently suffers from degradation in high temperature processes (HTP) such as crack, worse interfacial contact, and electrical properties, that is, annealing effect. To solve this problem, a kind of bifunctional SnO2 colloid is developed by using small molecular oxalate whose organic components can be removed clearly at a low temperature process (LTP). The c‐SnO2 and SnO2 mesoporous layer (m‐SnO2) derived from the fresh and aged sols with the same colloid show no annealing effect, decreasing oxygen vacancy, and adsorbing water on increasing annealing temperature. The champion devices of LTP and HTP SnO2 planar perovskite solar cells (PSCs) achieve, respectively, stabilized photoelectric conversion efficiencies (PCEs) of 20.74% and 20.70%. In contrast, the performance of champion devices of their mesoporous counterparts is significantly improved, showing nearly hysteresis free character with stabilized PCEs of 22.40% and 22.37%, respectively. The inclusion of m‐SnO2 plays a role of an energy bridge, improving electrons collection efficiency, which is supported by photoluminescence and transient photoluminescence characterizations. HTP SnO2 mesoporous PSCs can preserve 97.6% and 80% of their initial PCEs after aging for 25 weeks and 8‐h irradiated/16‐h dark cycle within 104 h. The high stability of HTP SnO2 PSCs may ascribe to low oxygen vacancy and adsorbed water of HTP SnO2.

Layer-selective functionalisation in mesoporous double layer via iniferter initiated polymerisation for nanoscale step gradient formation

Functionalisation of technological nanopores and investigation of their transport properties have attracted considerable interest from scientific as from technological point of view, among others due to their potential regarding molecular transport design. Asymmetric design of nanopore structure and functionalisation is expected to trigger increased and directed transport of ionic species. Based on this motivation, we demonstrate a layer-selective polymer functionalisation in a mesoporous double layer thin film to generate nanoscale step gradient architectures with asymmetric charge distribution by taking advantage of co-condensation and polymer modification techniques. Thereby, mesoporous silica and co-condensed mesoporous amino silica thin films are combined to double layered films with a film thickness of 300 – 400 nm in both sequential arrangements, respectively. Iniferter initiated polymerisation is used to selectively functionalise only the amino silica layer with polymers such as poly(2-(methacryloyloxy)ethyltrimethylammonium chloride) (PMETAC) in a grafting from approach. Investigation of the ionic pore accessibility of the mesoporous double layered films before and after layer-selective polymer functionalisation shows that the ionic pore accessibility is dominated by the bottom layer when overcoming the electrostatic repulsion of the top layer.

Synthesis of a novel SnO2/graphene-like carbon/TiO2 electrodes for the degradation of recalcitrant emergent pharmaceutical pollutants in a photo-electrocatalytic system

Photo-electro catalysis (PEC) has emerged as an efficient, sustainable, and green technology for the treatment of recalcitrant compounds, where anode plays a critical role. Novel preparation methods for anodes as catalysts should be considered in order to achieve larger active sites and diverse oxidants production, which can directly enhance the degradation performance. Therefore, in this work, a new cheap and green electrode material modification or synthesis method was studied. A graphene-like carbon mesoporous layer and SnO2 layer over TiO2 was produced and it resulted in higher porosity and stability of the electrode. This led to dominating advantage on photo/electrocatalytic activity and degradation performances. Synthesized electrodes attribute better charge separation and it was analyzed by electrochemical characterization. Hydroxyl radicals and superoxide (O2−) radicals were dominant oxidants in the degradation process based on the catalytic and degradation mechanism. However, the synergistic effect of photo and electro-catalytic degradation performances shrank under unoptimized PEC operational parameters. Therefore, the effect of various PEC parameters for the degradation of emerging pollutants was optimized. It was found that 90% degradation of emergent pollutants was achieved at optimized PEC operational parameters within 60 min of reaction time. Intermediates via PEC degradation of emerging pollutants were identified and a possible removal pathway was thus proposed. The three-dimensional SnO2-G-TiO2 electrodes hold great potential for PEC treatment of wastewater treatment.

Mesoporous TiO2 electron transport layer engineering for efficient inorganic-organic hybrid perovskite solar cells using hydrochloric acid treatment

We demonstrated effects of wet chemical processes using hydrochloric on crystallite structures, optical and electronic properties, and surface morphology of TiO2 thin films and enhancement in photovoltaic performance of perovskite solar cell using HCl-treated mesoporous TiO2 electron transport layers (ETLs). By treating mesoporous TiO2 thin films with HCl, hydroxyl groups on the surface were chemically neutralized and the film porosity was enhanced. Furthermore, the crystallite structure analyses indicated that CH3NH3PbI3 perovskite thin films deposited on the HCl-treated compact and mesoporous TiO2 ETLs possessed the relatively high crystallization along with avoiding formation of unexpected PbI2 crystals. As a result, the best power conversion efficiencies of devices using the HCl-treated mesoporous TiO2 ETLs were improved to 18.4% under forward bias scans.

Characteristics of Perovskite Solar Cells with ZnGa2O4:Mn Phosphor Mixed Polyvinylidene Fluoride Down-Conversion Layer

To reduce the manufacturing cost of perovskite solar cells, soda-lime glass and transparent conducting oxides such as indium tin oxide and fluorine-doped tin oxide are the most widely used substrates and lighttransmitting electrodes. However, the transmittance spectra of soda-lime glass, indium tin oxide, and fluorinedoped tin oxide show that all light near and below 330 nm is absorbed; thus, with the use of these substrates, light energy near and below 330 nm cannot reach the perovskite light-absorbing layer. It is expected that the overall solar cell can be improved if the wavelength can be adjusted to reach the perovskite solar cell absorbing layer through down-conversion of energy in the optical wavelength band. In this study, a polyvinylidene fluoride transparent film mixed with a ZnGa2O4:Mn phosphor was applied to the incident side of the perovskite solar cell with the intent to increase the light conversion efficiency without changing the internal bandgap energy and structure. By adding a phosphor layer to the external surface of PSC exposed to incident light, the efficiency of the cell was increased by the down-conversion of ultraviolet light (290 nm) to the visible region (509 nm) while maintaining the transmittance. To manufacture the perovskite solar cell, a TiO2-based mesoporous electron transport layer was spin-coated onto the substrate. The perovskite layer used in this experiment was CH3NH3PbI3 and was fabricated on a TiO2 layer. Spiro-OMeTAD solution was spin-coated as a hole-transport layer.

Effect of surface morphology on the mesoporous silicon modified nanofiltration membranes for high rejection performance

A new method to prepare composite nanofiltration membrane directly and efficiently by controlling the pore structure and surface morphology of the membrane is proposed in this paper. The fabrication of mesoporous silicon modified polysulfone blend membranes is via a phase inversion method. The structural morphology, surface functional group analysis, elemental analysis, hydrophilicity, chargeability, and nitrogen pollutant (ammonia nitrogen, nitrate nitrogen, total nitrogen) rejection properties of the modified membranes were found to be dependent on the amount of mesoporous silicon incorporated. The combination of the mesoporous silicon framework layer can not only effectively improve the surface structure of the modified membrane with a narrow pore size distribution but also increase the rejection of nitrogen pollutant compared with the pure NF membranes. The mesoporous material can absorb and storage the nitrogenous solution to facilitate the following interfacial polymerization, as well as induce the change of pore radius and surface structure. Compared to those pure NF composite membranes, the modified blend membranes exhibit increased water permeation flux as high as 29.09 L m−2 h−1 at 0.2 MPa. The results show that the optimum doping amount of mesoporous silicon is in the range of 0.5%-1.0%. Characterization studies demonstrated that the addition of the mesoporous silicon leads to decreased membrane pore size. Then, due to the enhanced hydrophilicity of carboxyl and hydroxyl groups on the surface, the electrostatic repulsion between the functional groups and nitrogen pollutant molecules in the membrane results in the enhanced rejection of nitrogen pollutants.

Annealing effects on interdiffusion in layered FA-rich perovskite solar cells

Annealing is one of the processing methods that are used for the fabrication of defect-free, photoactive perovskite films with compact grains in highly efficient and stable perovskite solar cells (PSCs). Thus, the annealing temperature is a key parameter for the control of the interdiffusion (of constituent elements) in photoactive films. In this paper, we present the results of a systematic study of the effects of annealing on the interdiffusion of constituent elements in efficient formamidinium-based PSCs. We also explore the effects of annealing-induced interdiffusion on layer microstructures, local strains, and the optoelectronic properties of perovskite films. We observe a dramatic upward diffusion of tin (Sn) and titanium (Ti) from fluorine-doped tin oxide and titanium dioxide (TiO2) to the perovskite films. We also observe a downward diffusion of lead (Pb) and iodine (I) from the perovskite films to the mesoporous layer of the electron transporting layer (ETL), after annealing at temperatures between 100 and 150 °C. The diffused I substitutes for Ti in the ETL, which improves the optoelectronic properties of the films, for annealing temperatures between 100 and 130 °C. The annealing-induced interdiffusion that occurs at higher temperatures (between 140 and 150 °C) results in higher levels of interdiffusion, along with increased local strains that lead to the nucleation of pores and cracks. Finally, the implications of the results are discussed for the design of PSCs with improved photoconversion efficiencies and stability.

Printed-Circuit-Board (PCB) Based Multiplex Sensor for Ion Sensing

Combining electrochemical sensing with microfluidic system presents an attractive approach for in vitro study of physiology and pathophysiology (e.g. organ-on-chip platform) [1] and for inline monitoring of environmental parameters (e.g. water quality) [2]. Ion-selective electrodes (ISE) are potentiometric sensors that measure activities of ions. They offer a simpler analytical method compare to voltammetric sensors or ISFETs. Solid-state ISEs differ from conventional ISEs in that the inner filling solution is replaced by a solid contact material. The removal of liquid compartment can make such sensor more durable and flexible, enabling it to be integrated with microfluidic device. In this work, we fabricated and evaluated a multiplex ion sensing platform by modifying the printed circuit board with solid-state ISEs. The choice of PCB platform allows straightforward multiplexing of electrodes and interfacing with downstream electronics by leveraging standardized PCB technology, which can also be cost effective in terms of fabrication. ISEs for potassium (K+) and nitrate (NO3-) approximately 1.5 mm in diameter were prepared by coating polymeric membrane and mesoporous carbon layers as the solid contact on a pre-patterned transfer tape. The electrode response was significantly stabilized by casting the membrane away from the underlying metal pads. The stabilizing effect was attributed to the increase of effective surface area of mesoporous carbon between membrane and conducting metal. The multiplex sensor was further integrated with a 3D printed microchamber for onchip analysis (Figure 1A). The K+ and NO3- electrodes displayed near-Nernstian slopes of 53 and -50 mV/dec (vs. Ag/AgCl/0.01 M Cl- reference) in KNO3 solutions, respectively. Despite some noise and baseline drift, both electrodes showed reasonable stability and reversibility upon switching solution (Figure 1B). The sensor can be stored dry between measurements. The slope of K+ electrode decayed over time, while NO3- electrode maintained sensitivity for at least one week. The slope decrease was likely due to the diffusion of ion-exchanger (tetraphenylborate) into the surrounding adhesive tape. During integration with the microchamber, the K+ electrode was also found subject to the bonding adhesive between the chamber and transfer tape, where possible reaction and/or degradation of the ion exchanger has caused complete loss of electrode response. Nevertheless, with further improvement, the PCB based multiplex ISEs provides a promising tool for ion sensing in many biomedical and environmental applications.

Porous TiO2 thin film-based photocatalytic windows for an enhanced operation of optofluidic microreactors in CO2 conversion

SummaryUsing a photocatalytic window can simplify the design of an optofluidic microreactor, providing also a more straightforward operation. Therefore, the development of TiO2 coatings on glass substrates seems appealing, although a priori they would imply a reduced accessible area compared with supported nanoparticle systems. Considering this potential drawback, we have developed an endurable photocatalytic window consisting on an inner protective SiO2 layer and an outer mesoporous anatase layer with enhanced surface area and nanoscopic crystallite size (9–16 nm) supported on a glass substrate. The designed photocatalytic windows are active in the CO2-to-methanol photocatalytic transformation, with maximum methanol yield (0.52 μmol·h−1·cm−2) for greatest porosity values and minimum crystallite size. Compared with benchmark supported nanoparticle systems, the nanoscopic thickness of the coatings allowed to save photoactive material using only 11–22 μg·cm−2, while its robustness prevented the leaching of active material, thus avoiding the decay of performance at long working periods.

Characterization of Thin MAPb(I1–xBrx)3 Alloy Halide Perovskite Films Prepared by Sequential Physical Vapor Deposition

Lead iodide (PbI2)-rich methylammonium lead bromide-iodide (MAPb(I1–xBrx)3) thin-films were prepared by sequential physical vapor deposition of methylammonium lead tri-bromide (MAPbBr3) on methylammonium lead tri-iodide (MAPbI3) bottom layer. The structural, optical, morphological, and electrical properties of the thin-films were studied as the thickness of methylammonium bromide (MABr) was increased from 300 to 500 nm. X-ray diffractograms confirmed transformation of tetragonal MAPbI3(x is 0.0) to the cubic-like structure of MAPbBr3 (x is 1.0) as MAPb(I1–xBrx)3 (x = 0.89–0.95) and PbI2 were formed. The bromine mole ratio x decreased as MABr thickness increased. UV-Vis absorption spectra showed that the bandgap of the thin alloy film decreased from 2.21 to 2.14 eV as x decreased. Scanning electron micrographs depicted densely packed grains that entirely covered the substrate and contained very few pinholes. The average grain size increased from 150 to 320 nm as x decreased. Electrical properties showed high charge carrier mobility that increased linearly with MABr thickness. FTO/MAPb(I1–xBrx)3/Au devices using fluorine-doped tin oxide (FTO) as substrate and gold (Au) as contacts were fabricated and current-voltage characteristics were determined. Space-charge-limited current theory was applied to charge carrier mobility and trap density of MAPb(I1–xBrx)3 thin-films. The charge carrier mobility increased as x decreased. The power conversion efficiency (PCE) of FTO/MAPbBr3/Au, FTO/MAPb(I0.11Br0.89)3/Au and FTO/MAPbI3/Au solar cells were 0.56, 0.62, and 1.15%. Devices including titanium dioxide compact layer (c-TiO2) and titanium dioxide mesoporous (m-TiO2) layer as electron transport layers were also fabricated for the application of Mott-Shottky (M-S) theory. Analyses of dark current-voltage and capacitance-voltage curves of FTO/c-TiO2/m-TiO2/MAPb(I0.11Br0.89)3 solar cells revealed a sizeable built-in voltage (Vbi) of 1.6 V and an accumulation of charge at interfaces for voltages greater than 0.2 V, respectively. Similar analyses for FTO/TiO2/MAPbI3/Au showed a small Vbi of 0.7 V and no charge carrier at interfaces. The work paves a way for reproducible growth of MAPb(I1–xBrx)3 for solar cells and sheds more light on the degree of ion migration in mixed halide and pure halide perovskites.

Low-Frequency Dielectric Relaxation in Structures Based on Macroporous Silicon with Meso-Macroporous Skin-Layer.

The spectra of dielectric relaxation of macroporous silicon with a mesoporous skin layer in the frequency range 1–106 Hz during cooling (up to 293–173 K) and heating (293–333 K) are presented. Macroporous silicon (pore diameter ≈ 2.2–2.7 μm) with a meso-macroporous skin layer was obtained by the method of electrochemical anodic dissolution of monocrystalline silicon in a Unno-Imai cell. A mesoporous skin layer with a thickness of about 100–200 nm in the form of cone-shaped nanostructures with pore diameters near 13–25 nm and sizes of skeletal part about 35–40 nm by ion-electron microscopy was observed. The temperature dependence of the relaxation of the most probable relaxation time is characterized by two linear sections with different slope values; the change in the slope character is observed at T ≈ 250 K. The features of the distribution of relaxation times in meso-macroporous silicon at temperatures of 223, 273, and 293 K are revealed. The Havriliak-Negami approach was used for approximation of the relaxation curves ε″ = f(ν). The existence of a symmetric distribution of relaxers for all temperatures was found (Cole-Cole model). A discussion of results is provided, taking into account the structure of the studied object.

Effect of TiO<sub>x</sub> and TiO<sub>2</sub> Layer on the Photovoltaic Property of BiOI Films

This study aims to investigate the impact of mesoporous and compact layers, like TiO2 and TiOx on the photovoltaic performance of bismuth oxyiodide (BiOI) films. BiOI thin films were prepared using the spin-coating method for 10 cycles onto FTO glass, FTO/TiOx, FTO/TiO2, and a combination of FTO/TiOx-TiO2 layer. Then, the resulted films were characterized on their optical, structural, and photovoltaic properties. By adding the TiOx or TiO2 layer into the cell, it resulted in the shifting of UV-Visible absorbance to a longer wavelength. On the structural property analysis, Raman spectra showed an overlapping peak among TiOx, TiO2, and BiOI films. Moreover, the solar cell was successfully developed using iodine electrolyte and Pt-counter electrode. By the photovoltaic analysis, it was known that the combination of those layers of metal oxide nanomaterials could give a slight improvement on the short-current density and open-circuit voltage of BiOI thin films. Therefore, the overall BiOI photovoltaic parameter was enhanced.

Surface Plasmons and Visible Light Iniferter Initiated Polymerization for Nanolocal Functionalization of Mesoporous Separation Layers

Although the technological relevance of mesoporous ceramic polymer hybrid materials is well accepted, missing functionalization concepts enabling 3D nanoscale local control of polymer placement into mesoporous materials, including thin films, and ideally using controlled polymerization techniques limit the application potential. Here, nanolocal functionalization of mesoporous separation layers using controlled, visible light iniferter initiated polymerization allowing responsive polymer functionalization locally limited to the irradiated spot is introduced. Thereby, two visible light sensitive iniferters, s-p-trimethoxysilylbenzyl-S´-dodecyltrithiocarbonate and 4-cyano-4-((dodecylsulfanylthiocarbonyl)sulfanyl)pentanoic acid, are developed for polymer functionalization of mesoporous films in a grafting from and a grafting through approach. 3D nanolocal polymer placement close to the proximity of the plasmonic field source is demonstrated by combining these visible light iniferter initiated polymerizations with optical near field modes, such as localized surface plasmon resonance (LSPR). As the location of the LSPR in mesoporous films can be controlled by placing metal alloy nanoparticles into these films and film thicknesses can be adjusted, this strategy is applied for precise positioning of polymers into mesoporous films with nanolocal control in three dimensions and thus reduces the gap in precision of functional group positioning between technological and biological nanopores.

Immersion-plated palladium nanoparticles onto meso-porous silicon layer as novel SERS substrate for sensitive detection of imidacloprid pesticide

Herein, we demonstrate the effectiveness of surface-enhanced Raman scattering (SERS) to detect trace concentration of potentially harmful imidacloprid pesticide. To achieve this ultimate objective, a rapid and highly effective methodology for the fabrication of active and stable porous silicon (PSi) plated palladium nanoparticles (PdNPs) SERS substrates by an electrochemical anodization and immersion plating routes was applied. The PSi layers were fabricated by the electrochemical anodization of a silicon wafer in ethanoic fluoride solution, followed by uniformly deposition of PdNPs via a simple immersion plating technique. The structural features and morphology of fabricated frameworks of PSi-Pd NPs have been investigated by field emission scanning electron microscopy (FE-SEM) with energy dispersive X-ray (EDX), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FT-IR) spectra. The PSi substrate demonstrates a meso-porous morphology with good distribution, good pore density and average pore sizes around 20 nm. The SERS performance of Si–Pd NPs and PSi–Pd NPs substrates has been examined taking imidacloprid (an insecticide) as a target analyte. The SERS signal of imidacloprid using PSi–Pd NPs substrate exhibited immense enhancement compared to the Si-Pd NPs substrate. The active substrate revealed excellent detectable performance with a concentration as low as 10–9 M imidacloprid and an enhancement factor (EF) of 1.2 × 105. This large EF is fundamentally ascribed to the combined effect of the electromagnetic improvement and charge transfer mechanisms. Additionally, no aging effect was observed for the present substrates kept in air for two weeks. Striking enhancement in Raman spectral signals obtained with the current PSi–Pd NPs substrates can provide a simple and smooth platform towards the sensitive detection of various target analytes.