Piranha Solution Research Articles

Molecular activation of fluoropolymer membranes via base piranha treatment to enhance transport and mitigate fouling – new materials for water purification

In this work, we introduce a reliable and direct method to activate fluoropolymers via integrating covalent labile ones for further modification. Basic piranha solution was used for the first time to functionalize polymeric surface with hydroxyl moieties. Subsequently, surfaces were modified with a varied molecular grafting. Materials were characterized and tested in several separation processes, including air-gap membrane distillation, osmotic membrane distillation, and microfiltration. This method deciphers surface architecture for various applications not only in membranes but also in variety of fields where functionalized fluoropolymers are employed. The work is also comparing membranes activated with acid and base piranha. The latter produced much more stable and resistant membranes with respect to the acid-treated ones. Systematic and material characterization on the molecular level, with the implementation of various spectroscopic, microscopic, and other techniques, was performed to prove and assess the generated, highly effective separation materials. The presented method opened the gate for fast and easy production of advanced functionalized fluoropolymers.

Investigation of the effect of different cleaning forces on Ce-O-Si bonding during oxide post-CMP cleaning

Ceria removal during the STI post-CMP cleaning process has recently become a serious concern to the semiconductor industries. It is known that ceria forms a strong Ce-O-Si bonding with the oxide surface that causes the difficulty in ceria removal. In this study, the bond formation and their removal were studied by polishing the oxide surface at pH 4 and pH 8 conditions, i.e. the pH of commercially formulated slurries. Ceria removal mechanisms were investigated through the use of different physical cleaning methods (megasonic and brush scrubbing) and chemical cleaning solutions such as standard cleaning solution 1 (SC1, a mixture solution of NH4OH, H2O2 and H2O), sulfuric acid, and hydrogen peroxide mixture (SPM), and diluted HF (DHF). It was found that ceria particles were removed easily at pH 4 polishing conditions as the electrostatic attraction is dominant than Ce-O-Si bond formation. However, at pH 8 conditions, particles were not removed due to strong bond formation. Only DHF and SPM cleaning conditions were able to remove the ceria particles due to the strong undercutting of oxide and dissolution of ceria particles, respectively. SPM could be the better choice as DHF would cause the surface roughness issues.

EFFECTS OF WETTABILITY ON DISPLACEMENT EFFICIENCY OF TWO-PHASE FLOW IN POROUS MEDIA

Displacement efficiency and displacement pattern of multiphase flow in porous media have a profound influence on many geo-energy applications such as geologic CO$_{2}$ sequestration and enhanced oil recovery. Wettability is one of the most important factors affecting the displacement pattern and displacement efficiency of multiphase flow in porous media. Here, we combined the glass microfluidics, inverted microscope and high speed CMOS camera to set up a visualization experimental system and modified the surface wettability of the glass microfluidics using the silanization treatment and piranha solution. Pore-scale visualization displacement experiments were conducted on five flow rates and two wetting conditions (hydrophilic and hydrophobic conditions) in glass microfluidics which are fabricated from the pore structure of natural sandstone. Experimental results show that the displacement pattern shifts from capillary fingering to compact displacement pattern both in the hydrophilic and hydrophobic media as the flow rate increases. Under lower flow rates, the capillary force plays the dominant role in the fluid invasion processes. The invasion finger width and the number of air clusters in hydrophilic media are both smaller than those in the hydrophobic media, but the maximum air cluster radius, the average cluster radius and the standard deviation of cluster radius are all greater under hydrophilic conditions. The results also demonstrate that the displacement efficiency under hydrophilic condition is significantly lower than that of hydrophobic conditions due to single-channel flow and by pass flow phenomena which both only occur in hydrophilic media. Finally, a modified capillary number was introduced in order to consider the role of wettability (contact angle) under favourable displacement. Then, a relationship between the displacement efficiency and the modified capillary number was proposed, which provides a potential and useful method for the prediction of displacement efficiency under different wetting conditions during favourable displacement.

A simple and reversible glass-glass bonding method to construct a microfluidic device and its application for cell recovery.

Compared with polymer microfluidic devices, glass microfluidic devices have advantages for diverse lab-on-a-chip applications due to their rigidity, optical transparency, thermal stability, and chemical/biological inertness. However, the bonding process to construct glass microfluidic devices usually involves treatment(s) like high temperature over 400 °C, oxygen plasma or piranha solution. Such processes require special skill, apparatus or harsh chemicals, and destroy molecules or cells in microchannels. Here, we present a simple method for glass-glass bonding to easily form microchannels. This method consists of two steps: placing water droplets on a glass substrate cleaned by neutral detergent, followed by fixing a cover glass plate on the glass substrate by binding clips for a few hours at room temperature. Surface analyses showed that the glass surface cleaned by neutral detergent had a higher ratio of SiOH over SiO than glass surfaces prepared by other cleaning steps. Thus, the suggested method could achieve stronger glass-glass bonding via dehydration condensation due to the higher density of SiOH. The pressure endurance reached over 600 kPa within 6 h of bonding, which is sufficient for practical microfluidic applications. Moreover, by exploiting the reversibility of this bonding method, cell recoveries after cultivating cells in a microchannel were demonstrated. This new bonding method can significantly improve both the productivity and the usability of glass microfluidic devices and extend the possibility of glass microfluidic applications in future.

Correction: High performance binder-free Fe–Ni hydroxides on nickel foam prepared in piranha solution for the oxygen evolution reaction

Correction for ‘High performance binder-free Fe–Ni hydroxides on nickel foam prepared in piranha solution for the oxygen evolution reaction’ by Cheol-Hwan Shin et al., Sustainable Energy Fuels, 2020, 4, 6311–6320, DOI: 10.1039/D0SE01253J.

The recovery of sulfuric acid from spent piranha solution over a dimensionally stable anode (DSA) Ti-RuO2 electrode

Piranha solution is a highly acidic mixture of sulfuric acid and hydrogen peroxide. The present study aimed at developing a dimensionally stable anode (DSA), made of titanium metal foil coated with Ruthenium Dioxide (RuO2), for the electrochemical oxidation of hydrogen peroxide in the presence of strong sulfuric acid under ambient conditions. Results showed that hydrogen peroxide in the piranha solution was fully degraded in 5 h under a constant current of 2 A (or current density of 0.32 A-cm-2). The oxidation kinetics of hydrogen peroxide followed the Langmuir-Hinshelwood model. The observed rate constant was a function of applied current. The initial current efficiency was 17.5% at 0.5 A (or 0.08 A-cm-2) and slightly decreased to about 13.5% at applied current between 1.3 and 1.5 A (or current density of 0.208 and 0.24 A-cm-2). Results showed the capability and feasibility of the electrochemical oxidation process for the recovery of sulfuric acid from the spent piranha solution in semiconductor industrial installations or general laboratories.

All-fiber phase modulator and switch based on local surface plasmon resonance effect of the gold nanoparticles embedded in gel membrane.

All-fiber modulators and switches have drawn great interest in the photonics domain, and they are applied in viable photonic and optoelectronic devices. In this work, with the assistance of an agarose membrane, aspherical gold nanoparticles are embedded on the surface of the microfiber treated with the piranha solution. An all-fiber Mach-Zehnder interferometer was used to realize a low-cost, low-loss, and conveniently prepared all-fiber phase modulator. By taking advantage of the local surface plasmon resonance effect of gold nanoparticles embedded in the agarose membrane, under the excitation of near-infrared region light, the gold nanoparticles were excited to change the effective refractive index of one arm of the Mach-Zehnder interferometer. A maximum phase shift of ∼6π at 1550 nm was obtained from the device. In addition, an all-optical switch was achieved with a rising edge time of 47 ms and falling edge time of 14 ms. The proposed all-fiber modulator and switch based on the local surface plasmon resonance effect of gold nanoparticles embedded in agarose membrane will provide great potential in all-optical fiber systems.

A SERS aptasensor based on AuNPs functionalized PDMS film for selective and sensitive detection of Staphylococcus aureus

In this study, a sensitive biosensor was developed based on aptamer functionalized polydimethylsiloxane (PDMS) film for the detection of Staphylococcus aureus (S. aureus) using surface-enhanced Raman scattering (SERS) technology. Initially, the surface of PDMS film was chemically modified by piranha solution and 3-Aminopropyltriethoxysilane (APTES), and then AuNPs-PDMS film was prepared by coating gold nanoparticles (AuNPs) through electrostatic interaction. Next, the aptamers were immobilized on the AuNPs-PDMS membrane via gold-sulfur bond to form the capture substrate. Meanwhile, gold-silver core-shell nanoflowers (Au@Ag NFs) modified with mercaptobenzoic acid (4-MBA) and aptamers were applied as a signal probe. In the presence of the target, the signal molecular probe and the capturing substrate specifically combined with the target and resulted in a sandwich structure “capture substrate-target-signal molecular probe”. Under the optimized experimental condition, the signal of 4-MBA at 1085 cm-1 was linearly related to the S. aureus concentration in the range of 4.3 × 10 cfu mL−1-4.3 × 107 cfu mL−1 (y = 326.91x-117.62, R2 = 0.9932) with a detection limit of 13 cfu mL−1. The method was successfully applied to spiked actual samples and a 92.5–110% recovery rate was achieved.

Planar Interdigitated Aptasensor for Flow-Through Detection of Listeria spp. in Hydroponic Lettuce Growth Media.

Irrigation water is a primary source of fresh produce contamination by bacteria during the preharvest, particularly in hydroponic systems where the control of pests and pathogens is a major challenge. In this work, we demonstrate the development of a Listeria biosensor using platinum interdigitated microelectrodes (Pt-IME). The sensor is incorporated into a particle/sediment trap for the real-time analysis of irrigation water in a hydroponic lettuce system. We demonstrate the application of this system using a smartphone-based potentiostat for rapid on-site analysis of water quality. A detailed characterization of the electrochemical behavior was conducted in the presence/absence of DNA and Listeria spp., which was followed by calibration in various solutions with and without flow. In flow conditions (100 mL samples), the aptasensor had a sensitivity of 3.37 ± 0.21 kΩ log-CFU−1 mL, and the LOD was 48 ± 12 CFU mL−1 with a linear range of 102 to 104 CFU mL−1. In stagnant solution with no flow, the aptasensor performance was significantly improved in buffer, vegetable broth, and hydroponic media. Sensor hysteresis ranged from 2 to 16% after rinsing in a strong basic solution (direct reuse) and was insignificant after removing the aptamer via washing in Piranha solution (reuse after adsorption with fresh aptamer). This is the first demonstration of an aptasensor used to monitor microbial water quality for hydroponic lettuce in real time using a smartphone-based acquisition system for volumes that conform with the regulatory standards. The aptasensor demonstrated a recovery of 90% and may be reused a limited number of times with minor washing steps.

Improvement in the performance of an electrochemical sensor for ethanol determination by chemical treatment of graphite

Abstract The present work describes the preparation and characterization of chemically treated graphite by different strategies and its use for the construction of nickel-based electrochemical sensors for ethanol determination. Chemical treatment of graphite powder was carried out under three different conditions: with nitric acid, with piranha solution (98% sulfuric acid and 30% hydrogen peroxide in the ratio of 70:30) and by the Hummers method. Treated and untreated graphite samples were characterized by scanning electron microscopy techniques (SEM), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), x-ray diffraction (XRD) and thermogravimetry (TG). Surface chemical groups were estimated by Boehm titration. Carbon paste electrodes were constructed using untreated and treated graphite and evaluated for adsorption of nickel ions. After that, exploring the catalytic proprieties of redox pair Ni(II)/Ni(III) the device was applied towards ethanol oxidation. From all chemical treatments evaluated, samples of graphite treated by the Hummers method presented the best analytical performance. Using the best set of experimental conditions, it was observed a linear dynamic range (LDR) between 50 and 1000 μmol L−1 with a sensitivity of 42.1 μA L mmol−1 and limit of detection (LOD) and quantification (LOQ) of 15 and 50 μmol L−1, respectively. The electroanalytical application of the sensor was performed for ethanol quantification in four distilled beverage samples (vodka, cachaca, pisco and whiskey) using amperometry. The obtained results agree with a comparative method at a confidence level of 95%. Repeatability studies for five different electrodes showed an RSD of less than 10%.

Waste engine oil derived porous carbon/ZnS Nanocomposite as Bi-functional electrocatalyst for supercapacitor and oxygen reduction

Abstract Herein, we report the effective conversion of waste automobile engine oil into porous activated carbon/ZnS nanocomposite. Initially, the waste engine oil was thermally decomposed under an argon atmosphere at 700 °C and followed by acid treatment with a 10% piranha solution to form activated carbon/ZnS (ACZS) nanocomposites. The ACZS was used as electrode active material for symmetric supercapacitor and electrocatalyst for oxygen reduction reaction (ORR) studies. It is interesting to note that, the ACZS electrode performed well for supercapacitor delivered a high specific capacitance of 241 F/g at 1 A/g current density. The symmetric supercapacitor cell fabricated using ACZS electrodes delivered a high specific energy and specific power of 13.8 Wh/kg and 4500 W/kg with an exceptional electrochemical stability of 95% for 10,000 cycles, respectively. The electrochemical RRDE studies shows higher ORR current density of ACZS electro-catalyst (4.46 mA/cm2) than that for the HiSPEC Pt/C catalyst (3.91 mA/cm2).

Effect of halloysite nanotubes on multifunctional properties of coaxially electrospun poly(ethylene glycol)/polyamide-6 nanofibrous thermal energy storage materials

Coaxial electrospinning of poly(ethylene glycol) (PEG)/polyamide 6 (PA6) was successfully used in development of nanofibrous thermal energy storage (TES) material. Halloysite nanotubes (HNTs) were introduced into the core/shell structured TES materials at various concentrations (0.5, 1, 3 and 5 wt. %). Surface activation of HNT was also conducted by piranha etching in order to increase the affinity between piranha-etched nanotubes (HNT-P) and PEG. The core/shell structured materials were characterized using SEM, FTIR, TGA, DSC, tensile and thermal cyclic tests. With incorporation of 3 wt. % HNT-P into the core/shell nanofibers, tensile modulus and latent heat of melting values were increased by 25 % and 21 %, respectively. Additionally, PEG encapsulation efficiency of the neat core/shell nanofibers was increased from 78 % to 96 % with 3 wt. % HNT-P addition. The neat core/shell samples preserved 88 %, whereas 3 wt. % HNT and HNT-P added nanofibrous samples preserved 94 % of their initial melting enthalpies.

Intrinsic properties of high-aspect ratio single- and double-wall anodic TiO2 nanotube layers annealed at different temperatures

In this work, we present the influence of thermal annealing on morphological, structural, electrical, optical, and photoelectrochemical properties of double- (DW) and single-wall (SW) TiO2 nanotube (TNT) layers. High-aspect ratio TNT layers with a thickness of ∼5 μm and ∼20 μm with an average inner diameter of ∼250 nm and ∼130 nm, respectively, were prepared via electrochemical anodization of Ti foil in two different fluoride containing ethylene glycol-based electrolytes. The inner wall of the native DW TNT layers was quantitatively removed via a mild pre-annealing followed by a selective etching treatment in piranha solution, yielding SW TNT layers. The obtained SW TNT layers annealed at 300–500 °C possess enhanced conductivity by 1–2 orders compared to their DW counterparts. The photoelectrochemical properties of SW TNT layers are enhanced compared to their DW counterparts in the annealing temperature range 300–800 °C. In principle, the SW TNT layers could be potentially favored to the DW TNT layers in electrical and photoelectrochemical applications due to their more superior intrinsic properties.

Influence of surface treatment on the structure and properties of proton-exchanged waveguides in lithium niobate

The influence of reverse proton exchange (RPE) and some types of surface pretreatment (exposure to Piranha or RCA-1 solutions or to HNO3+HF mixture) on the structure and properties of proton-exchanged layers has been studied in X-cut lithium niobate (LN). It has been shown that the rate of phase transitions in PE layers during RPE is greater than that during annealing at the same temperature. Pretreatment of LN surface before PE by Piranha or RCA-1 solutions slightly increases refractive index change Δne in the resulting waveguide, whereas pretreatment by HNO3+HF mixture decreases it.

Recovering Indium Tin Oxide Electrodes for the Fabrication of Hematite Photoelectrodes

Indium tin oxide (ITO) electrodes are widely used in basic and applied research as well as in commercial electronic devices. After a primary use, ITO electrodes are commonly wasted without further application. Herein, we recycled ITO electrodes previously used as anodes in organic photovoltaic devices in our group. These recycled electrodes were treated with piranha solution to obtain recovered ITO electrodes (ITOPS). Chemical and structural changes of ITOPS electrodes were evaluated using XPS, EDS, UV/VIS, XRD, SEM and cathodic polarization studies pointing out for a complete leach of indium from the structure leaving a conductive tin oxide-based electrode. Subsequently, these electrodes were used in the fabrication of hematite photoelectrodes by a two-step process of electrodeposition and annealing. Structural characterization of the deposited thin film was performed before and after annealing treatment with XDR, Raman spectroscopy and XPS. A hematite thin film deposited on an ITOPS substrate was successfully obtained from the thermal dehydration of akaganeite. SEM micrographs showed a homogeneous distribution of the hematite deposit. Under a 470 nm LED illumination, hematite photoelectrode achieved a photocurrent density of 223 μA cm−2 at 0.8 V vs SCE showing a potential second life for recycled ITO electrodes (ITOPS) as substrates for photoelectrocatalytic processes.

High performance binder-free Fe–Ni hydroxides on nickel foam prepared in piranha solution for the oxygen evolution reaction

A novel binder-free Fe–Ni hydroxide-loaded nickel foam (NF) electrode is prepared by simple corrosion of NF in a home-made piranha solution containing Fe3+ and exhibits remarkable electrochemical OER activity and long-term stability.

High Performance Binder-Free Fe-Ni Hydroxides on Nickel Foam Prepared in Piranha Solution for Oxygen Evolution Reaction

High Performance Binder-Free Fe-Ni Hydroxides on Nickel Foam Prepared in Piranha Solution for Oxygen Evolution Reaction

Hydrogen passivation of iron-acceptor pairs in boron and gallium co-doped crystalline silicon

The hydrogen (H) passivation behaviors of iron-acceptor (Fe-Ac) pairs in boron and gallium co-doped Czochralski silicon are studied. H atoms introduced by a piranha solution followed by reverse bias annealing can fully passivate the electric activity of Fe–B and Fe–Ga pairs. However, the passivation effect can be partially deactivated when annealed in 80 °C–200 °C and be reactivated when annealed at 250 °C. The temperature of the highest failure fraction for passivated Fe–B and Fe–Ga pairs are 80 °C and 200 °C, respectively. A mechanism was given that H atoms released from the dissociation of acceptor-hydrogen pairs can reactivate the passivation.

Ti3+ doped anodic single-wall TiO2 nanotubes as highly efficient photocatalyst

In this work, a two-step treatment of TiO2 nanotube (TNT) layers towards enhanced photocatalytic performance is presented. TNT layers with a thickness of ∼7 μm and an average inner diameter of ∼190 nm were prepared via electrochemical anodization of Ti foil in a fluoride containing ethylene glycol-based electrolyte. To improve the photocatalytic activity of the produced TNT layers a two-step post-treatment was conducted. First, the inner shell of the native double-wall TNT layers was removed via a mild pre-annealing followed by a selective etching treatment of the inner shell in piranha solution yielding single-wall TNT layers. Second, reduction via annealing in H2/Ar atmosphere was performed. The resulting Ti3+ doped single-wall TNT layers possess 100% enhancement of photocatalytic activity compared to their non-treated counterparts.

Bent-core liquid crystal-functionalised flexible polymer substrates for liquid crystal alignment

ABSTRACTA transparent flexible polymer film is chemically functionalised with a bent-core liquid crystal (BCLC) compound for effective alignment of the bulk BCLC sample at the substrate–LC interface. The surface attachment was achieved via a simple procedure which involved pre-treatment of the polymer film (commercial name: over head projector film) using piranha solution followed by chemically attaching the BCLC compound through silane condensation reaction. Surface characterisation of the unmodified and BC-modified flexible films was carried out through X-ray photoelectron spectroscopy (XPS), attenuated total reflectance fourier transform infrared (ATR-FTIR) spectroscopy, contact angle (CA) and atomic force microscopy (AFM) techniques. The BC-modified flexible substrates are analysed for their efficiency to orient the bulk LC sample. Remarkably, the chemically modified polymer substrates are highly efficient in vertically aligning both the BC and rod-like LC samples at the substrate–LC interface, in comparison to their unmodified counterparts. The described method is simple, reproducible, surface modified substrates are highly stable and more importantly reusable. The demonstrated method for the alignment of BCLCs advances a step forward towards the realisation of applications proposed for these fascinating compounds.