1M H3PO4 Research Articles

Phosphorous - Containing Activated Carbon Derived From Natural Honeydew Peel Powers Aqueous Supercapacitors.

The introduction of phosphorous (P), and oxygen (O) heteroatoms in the natural honeydew chemical structure is one of the most effective, and practical approaches to synthesizing activated carbon for possible high-performance energy storage applications. The performance metrics of supercapacitors depend on surface functional groups and high-surface-area electrodes that can play a dominant role in areas that require high-power applications. Here, we report a phosphorous and oxygen co-doped honeydew peel-derived activated carbon (HDP-AC) electrode with low surface area for supercapacitor via H3PO4 activation. This activator forms phosphorylation with cellulose fibers in the HDP. The formation of heteroatoms stabilizes the cellulose structure by preventing the formation of levoglucosan (C6H10O5), a cellulose combustion product, which would otherwise offer a pathway for a substantial degradation of cellulose into volatile products. Therefore, heteroatom doping has proved effective, in improving the electrochemical properties of AC-based electrodes for supercapacitors. The specific capacitance of HDP-AC exhibits greatly improved performance with increasing carbon-to-H3PO4 ratio, especially in energy density and power density. The improved performance is attributed to the high phosphorous doping with a hierarchical porous structure, which enables the transportation of ions at higher current rates. The high specific capacitance of 486, and 478 F/g at 0.6, and 1.3 A/g in 1 M H2SO4 electrolyte with a prominent retention of 98.5 % is observed for 2 M H3PO4 having an impregnation ratio of 1 : 4. The higher yield of HDP-AC could only be obtained at an activation temperature of 500 °C with an optimized amount of H3PO4 ratio. The findings suggest that the concentration of heteroatoms as surface functional groups in the synthesized HDP-AC depends on the chosen biomass precursor and the processing conditions. This work opens new avenues for utilizing biomass-derived materials in energy storage, emphasizing the importance of sustainable practices in addressing environmental challenges and advancing toward a greener future.

Utilization of Adsorbent Based on Rice Straw (<i>Oryza sativa</i>) for Cr(VI) Ions Reduction in Aqueous Solutions

In this study, we utilized an adsorbent based on rice straw for reducing hexavalent chromium ions (Cr (VI)) in an aqueous solution. The rice straw as adsorbent raw material was washed, dried, and powdered. Rice straw powder was heated at 450°C for 2 hours to obtain rice straw adsorbent. The adsorbent was activated with 1M H3PO4 for 4 hours. Characterization of the adsorbent was done using Fourier Transform Infra-Red (FTIR) method. FTIR spectra showed the presence of hydroxy, carboxylic, aromatic, and ether groups on the surface of the rice straw and the made adsorbent. The reduction of Cr (VI) ions in aqueous solutions was carried out using the adsorption batch method. The adsorption process was conducted in various the Cr (VI) solutions pH for 1-5 and variations in contact time for 5-720 minutes. The highest percentage reduction of Cr (VI) reached 66.90%. It has occurred at pH 2 and equilibrium at 600 minutes of contact time.

Analysis of biodiesel process from waste cooking oil using heterogeneous catalyst field snail shell (pila ampullacea)

Biodiesel is an alternative fuel in the form of Fatty Acid Methyl Ester (FAME) which can be renewed using vegetable oils and animal oils through esterification or transesterification processes. This study used waste cooking oil as a raw material for biodiesel with a CaO catalyst from the shells of field snails (Pila ampullacea) which were calcined for 4 hours at a temperature of 700°C. This experiment aim to study of the effect of temperature (55°C, 60°C, 65°C) and catalyst weight (4%, 6%, 8%), for 2 hours the transesterification process and the molar ratio of oil to methanol was 1:9. Crude Biodiesel from the transesterification process washed using dry washing method with activated coconut shell charcoal which has been activated using 1M H3PO4. Based on this research, the optimum yields about 91,5%-volume, were obtained in A2T2 with temperature 60°C and a catalyst weight of 6% with a biodiesel yield of 91.5%. The characteristics of the biodiesel produced were kinematic viscosity 3.32 cSt, density 863 Kg/m3, acid number 0.543%, iodine number 14.3%-mass, methyl ester content 169.12% and cetane number 43.28%-mass.

Response Surface Modelling and Optimization of Lead Adsorption from Wastewater Using Rice Husk Activated Carbon

Nigeria is renowned for its vast production of paddy rice, resulting in a significant volume of rice husk generation. Consequently, the conversion of these quantities of rice husk into beneficial applications is imperative to mitigate environmental pollution. The rice husk, procured from local millers in Zaria market, Nigeria, was subjected to thermal and chemical methods to produce activated carbon. The carbonization process involved heating at three different temperatures (300, 350 and 400 ℃) and subsequent mixing with 1M H3PO4 at a 1:2 ratio. Batch adsorption experiments were conducted, varying dosages of rice husk activated carbon (1 - 5 g), lead initial concentrations (10 - 60 mg/l), and carbonization temperatures (300 - 400 ℃). The Response Surface Methodology was utilized to model the adsorption capacities and removal efficiencies obtained. At carbonization temperature of 350 ℃, initial lead concentration of 60 mg/l, and adsorbent dosage of 3 g, the optimum removal efficiency and adsorption capacity 100% and 1.690 mg/g, respectively were observed. The veracity of the model equations was confirmed through the verification of the optimum adsorption conditions, with recorded percentage errors of 0.253% and 17.988%, for removal efficiency and adsorption capacity, respectively. The study's findings showed that rice husk activated carbon was highly effective in removing lead from wastewater. Furthermore, the model equations demonstrated reliability in forecasting the responses, and the optimum conditions were deemed valid.

Corrosion of Titanium Alloys Anodized Using Electrochemical Techniques

The anodization of titanium has been an excellent option for protecting titanium and its alloys from corrosive environments such as acids and chloride systems, by generating a homogenous oxide layer. The objective of the current investigation was to evaluate the electrochemical corrosion behavior of alloys Ti-6Al-2Sn-4Zr-2Mo and Ti-6Al-4V anodized in 1M H2SO4 and H3PO4 solutions at a current density of 2.5 × 10–3 A/cm2. The anodization’s electrochemical characterization was achieved in NaCl and H2SO4 at 3.5% wt. electrolytes. Scanning electron microscopy (SEM) was employed to determine the anodized thickness and morphology. Cyclic potentiodynamic polarization (CPP) and electrochemical impedance spectroscopy (EIS), based on ASTM G61-86 and G106-15 Standards, were the electrochemical techniques mainly employed. The anodized samples presented a change in Ecorr values and a higher passivation zone. The EIS plot showed a higher resistance for samples anodized in H3PO4 and Ti-6Al-2Sn-4Zr-2Mo.

MODELLING AND OPTIMIZATION OF CADMIUM REMOVAL FROM WASTEWATER ONTO SUGARCANE BAGASSE ACTIVATED CARBON

The presence of sugarcane bagasse as an agricultural waste in the environment is a cause for concern as it defaces the environment. It is bulky and difficult to manage. This prompt the need to research into the reuse of sugarcane bagasse in a more rewarding way, thereby saving the environment from its litters. In this study, Sugarcane bagasse was collected from Gaskiya Road in Zaria and converted to activated carbon using thermal and chemical methods. The Sugarcane bagasse was divided into three portions and carbonized at temperatures of 300, 325 and 350oC and then chemically modified with 1M H3PO4 acid at ratio of 1:2. Batch adsorption experiments were carried out using three input variables: adsorbent dosages of 0.2 - 1.0 g; initial cadmium concentrations of 5 - 25 mg/l and carbonization temperatures of 300 - 350 oC with the corresponding output variables of removal efficiency (X1) and adsorption capacity (X2). The experimental data were modeled, optimized and validated using Response Surface Methodology (RSM). The optimum operating conditions for adsorption of cadmium onto sugarcane bagasse activated carbon were: carbonization temperature of 300 oC, initial cadmium concentration of 25 mg/l and adsorbent dosage of 1.0 g with the corresponding optimized removal efficiency and adsorption capacity of 100% and 2.5mg/g, respectively. The optimized removal efficiency and adsorption capacity were validated and the errors of 0.000 and 0.009%, respectively were recorded. It was concluded that sugarcane bagasse was effective in the removal of cadmium from wastewater and hence its reuse as an adsorbent in wastewater treatment is a viable waste management option. Also the model developed had proven to be valid in predicting the output variables.

Porous Surface State Analysis of Anodized Titanium for Biomedical Applications

In this work, pure Ti was anodically oxidized using 1M H3PO4 + 2–10 pct HF electrolytes at 10 V vs open circuit potential (OCP). The structure of the anodized samples’ surfaces was investigated using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and scanning electron microscopy (SEM). The results show the presence of titanium dioxide (TiO2) and titanium hydrogen phosphate (Ti(HPO4)2) in the surface layer. Due to the chemical composition and properties that the materials have, they do not pose a threat and support the osseointegration process. The rough and porous anodic oxide morphology shown by the AFM is useful for tissue growth, as well as for improving corrosion resistance. The XPS confirms that the short anodization results in thin anatase-type TiO2, which is a candidate for hard tissue implant applications. The corrosion is improved after oxidation in 1M H3PO4 + 2 pct HF electrolyte for 15 minutes. The wetting analysis shows hydrophilic properties and suggests good bioadhesion of the anodically oxidized surface. The surface supports osteoblast cell proliferation, indicating that the material has a surface state appropriate for hard tissue implant applications.

Morphology, Topography and Wettability of CP-Ti after Anodization Process for Biomedical Applications

Titanium (Ti) is widely applied for biomedical implants owing to its exceptional properties such as biocompatibility, corrosion behavior and wear resistance. However, these implants may undergo from some unfavorable results coming from the lack of their surface properties. Therefore, the development of required surface properties of Ti implants is an important issue. In particular, Ti dioxide (TiO2) nanotubes (NTs) have displayed auspicious features to modulate the biological responses of Ti. In this study, the anodization process was carried out onto the surface of commercial pure titanium (CP-Ti) substrate in an electrolyte contains a 0.8M NaF in 1M H3PO4 at constant applied voltage of 10 V for 30, 90, and 150 min. The structure and morphology, topography, along with adhesion strength of both non-anodized and anodized Ti samples have been investigated

FTIR, SEM and XRD analysis of activated carbon from sago wastes using acid modification

Activated charcoal bio adsorbent is a method that can be developed because the raw material is easy to obtain and does not require large costs such as processing sago. The stages of making activated carbon include the stages of dehydration, carbonization, and extraction of silica using 4% NaOH solution (1:10). The activation stage successively used 250 mL of 1M NaCl, 1M MgCl2, 1M CaCO3, 1M K2Cr2O7 and the addition of 100 mL of 1M HNO3, 3% H2O2, 1M H3PO4 and 4NH2SO4 respectively. The activation process uses a water bath at 700°C for 3 hours. In the conventional carbonization stage in a vacuum used drum for 1x24 hours. Physicochemical analysis of activated carbon products, namely moisture content, ash content, pH, Activated Carbon Adsorption Test against Iod Test and methylene blue. FT-IR analysis showed a wide band of 3442.94 cm‒1 to 3415.93 cm‒1 which showed the free O-H strain vibrations of the OH group in the cellulose molecule. 1178.51 cm‒1, –1039.53 cm‒1, -1024.20 cm‒1, C-C and C-O-C glycosidic ether band. SEM data describes the differences in the surface morphological structure of each sample and is supported by XRD data.

Nanotubular Oxide Layer Formed on Helix Surfaces of Dental Screw Implants

Surface modification is used to extend the life of implants. To increase the corrosion resistance and improve the biocompatibility of metal implant materials, oxidation of the Ti-13Nb-13Zr titanium alloy was used. The samples used for the research had the shape of a helix with a metric thread, with their geometry imitating a dental implant. The oxide layer was produced by a standard electrochemical method in an environment of 1M H3PO4 + 0.3% HF for 20 min, at a constant voltage of 30 V. The oxidized samples were analyzed with a scanning electron microscope. Nanotubular oxide layers with internal diameters of 30–80 nm were found. An analysis of the surface topography was performed using an optical microscope, and the Sa parameter was determined for the top of the helix and for the bottom, where a significant difference in value was observed. The presence of the modification layer, visible at the bottom of the helix, was confirmed by analyzing the sample cross-sections using computed tomography. Corrosion tests performed in the artificial saliva solution demonstrated higher corrosion current and less noble corrosion potential due to incomplete surface coverage and pitting. Necessary improved oxidation parameters will be applied in future work.

Nanoscale Electropolishing of High-Purity Aluminum with a Deep Eutectic Solvent

Recent advancements in electrochemical polishing have minimized surface roughness and enhanced conductivity properties of high-purity (>99.9% composition) aluminum surfaces in ways that machine polishing and simple chemical polishing cannot compare. Aluminum metals have a high propensity to deliver powerful electric charges with little resistance, thus making them effective for a wide range of electroconductivity experiments. The effects of an acid-free ionic liquid electrolyte solution were tested to determine potential energy thresholds during electropolishing treatments based upon temperature, experiment duration, current, and voltage.High purity aluminum metal specimens were used in electropolishing treatments with an acid-free ionic liquid electrolyte prepared from quaternary ammonium salts as an environmentally friendly alternative to acid-based solutions. An ionic liquid solution was formed from ethylene glycol and choline chloride combined in a 2:1 ratio. Similar ionic liquid solutions have been successfully employed to electropolish metal alloys, but little research has been conducted with this approach to polish rare earth metals like aluminum (1-5). Linear sweep voltammetry and chronoamperometry tests were initially used to determine ideal conditions for electrochemical polishing, while Atomic Force Microscopy revealed nanoscale effectiveness of the ionic liquid relative to an industry standard acid polishing treatment of 1 M Phosphoric Acid. Surface characterization via root mean squared roughness before and after electrochemical polishing treatments in 10x10 µm sample regions were used to estimate polishing efficiency throughout a 15-minute treatment period at 70 deg C and an average voltage of 2V.Results from electropolishing treatments in the ionic liquid electrolyte revealed a significant change in root mean squared roughness from 159.31 nm to 26.649 nm and resulted in an overall mass loss of 0.0394 g. A change of 132.661 nm during the 15-minute treatment resulted in an electropolishing efficiency of 83.272% and a shiny mirror finish 6x smoother than the same aluminum surface prior to treatment.Comparatively, the phosphoric acid electropolishing treatment yielded only a nominal improvement in root mean squared roughness of 97.786 nm, yet resulted in a greater mass loss of 0.0458 g for a lower smoothing efficiency rating of 38.546%. The electropolishing rate via the Phosphoric Acid solution is greater, yet the efficiency is less favorable due to significant pitting at low current densities (Figure 1). Hydrogen contamination was observed to adversely impact the overall root mean squared roughness of all sampled areas, yet this may be remedied via costly degassing treatments at temperatures of greater than 800 deg C to achieve more comparable results to the ionic liquid solution by mitigating some of the pitting and bubbling caused by hydrogen attack. In this study, a green polishing solution was prepared from simple inorganic salts, alkyls, and other organic solvents. This eco-friendly solution produced polished surfaces superior to those surfaces treated with industry standard acid electrochemistry treatments of 1M H3PO4.

Cotton textile waste valorization for removal of tetracycline and paracetamol alone and in mixtures from aqueous solutions: Effects of H3PO4 as an oxidizing agent

The use of waste and by-products locally available in large quantities and at low cost as adsorbents can be considered an appropriate approach for improving waste management and protecting the environment. Cotton textile waste was used to prepare adsorbents (MC) via pyrolysis followed by a chemical modification with H3 PO4 . MC samples were characterized by scanning electron microscopy, FTIR spectroscopy, and N2 adsorption-desorption isotherm. The results revealed that MC treated with 1M H3 PO4 (MC1 ) showed an excellent adsorption performance. The single and binary adsorption of tetracycline (TC) and paracetamol (Pa) onto MC1 were studied. In a single system, TC was better adsorbed than Pa and maximum adsorption capacities qm are 87.7mg/g and 62mg/g, respectively. The adsorption follows the Langmuir and pseudo-second-order kinetic models. For a binary system, the experimental data indicate that Pa (44.04mg/g) is better adsorbed than TC (24.13mg/g). Adsorption equilibrium data of TC and Pa evaluated by the selectivity extended-Langmuir model in which selectivity factor was introduced provided good correlation results with the binary adsorption data. Cotton textile waste is potentially promising for the preparation of effective adsorbents for the removal of pharmaceutical residues in aqueous solutions. PRACTITIONER POINTS: Valorization of cotton textile waste into adsorbents. Adsorbents were prepared by pyrolysis at 600°C followed by chemical modification in the presence of H3 PO4 . Removal of tetracycline (TC) and paracetamol (Pa) alone or in mixtures by adsorption. Adsorbent showed high-capacity adsorption of the TC and Pa even in a mixture from solutions at low concentrations. The Langmuir and selectivity extended-Langmuir models describe the adsorption of TC and Pa alone and in mixtures, respectively.

Surface Observation of Plasma Electrolytic Oxidation-Treated Ti-6Al-4V Alloy After 2-Step Nano-Mesh Formation.

The purpose of this study was to investigate the surface observation of PEO-treated Ti-6Al-4V alloy after 2-step nano-mesh formation was investigated by FE-SEM, EDS, and XRD. Anodic oxidation treatment was performed on the electrolyte containing 0.8 wt.% Na/F and 1M H₃PO₄ to form a nanotube structure on the Ti-6Al-4V alloy. After removing the nanotube layer, PEO-treatment was performed on the electrolyte containing Mg and Zn ions. After forming the nanotubes, the nanomesh surface was obtained by removing the layer, and the surface roughness increased with cycle number of nanotube formation. Also, as the number of nanotubes increased, the anatase peak increased.

Effect of surface fluorination on the hydrophilicity of the anodised films for dental implant applications

ABSTRACT Hydrophilicity is an important factor for dental implant applications. It can improve the implant surface-blood interaction resulting in improved implant osseointegration. The aim of this research was to investigate the effect of fluoride on the hydrophilicity of the anodised films. The anodised films were performed by two-step anodisation at low current density in mixing solution of 1M H3PO4 (20 ml) + 80% v/v C2H5OH (20 ml) with different NaF concentrations of 0.25, 0.5, 1, 2, 4 wt % (20 ml). The two-step anodisation using 2 mA/cm2 in 1M H3PO4 + 80% v/v C2H5OH + 4 wt % NaF could enhance hydrophilicity to the anodised films due to hydroxyl groups, surface roughness and the F−ions incorporated into the anodised films. Therefore, a high content of F−ions (4 wt % NaF) was shown to promote hydrophilicity of the anodised films.

Green approach to corrosion inhibition of stainless steel in phosphoric acid of Artemesia herba albamedium using plant extract

Essential oil from aerial parts of Artemisia herba-alba from Morocco was hydrodistilled and its chemical composition oil was investigated by capillary GC and GC/MS. The major components were 1,8-cineole (35.6%) and camphor (24.1%). Artemisia herba-alba essential oil AHAO was tested as corrosion inhibitor of stainless steel (SS) in 1M H3PO4 using potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy measurements (EIS) and scanning electronically microscopy (SEM) studies. The results obtained showed that the essential oil of Artemisia reduces the corrosion rate. Tafel polarization method indicates that the plant extract behaves as a mixed type inhibitor. The inhibition efficiency increased with inhibitor concentration to attain 88% at 1g.L−1 of oil at 298K. Nyquist diagrams obtained from impedance studies provide results confirming the anti-corrosion effect of the studied plant. The temperature effect on the corrosion behavior of (SS) in 1M H3PO4 without and with AHAO at 1g.L−1 was studied in the temperature range from 298 to 353K. Thermodynamic parameters suggested that the adsorption is spontaneous and exothermic process and support physical adsorption mechanism. The experimental data fits well into the Langmuir adsorption isotherm model. SEM/EDS studies provide the confirmatory evidence for the protection of (SS) by the green inhibitor. The results obtained from these methods used are in good agreement.

Surface modification to develop hierarchical micro/nano topography on titanium based medical implants

Self-organized nanostructured TiO2 layers were developed on micro rough planar, cylindrical, and threaded surfaces of Ti6Al4V alloy by electrochemical anodization (EA) performed in phosphate-fluoride solution (1M H3PO4 with different HF additions) by using different process parameters (electrolyte concentration, anodization potential U, potential ramp Ur, and sample rotational speed n). Optical microscopy and scanning electron microscopy (SEM) was used to evaluate the morphology of the oxide layers. Nanostructured oxide layers with nanotubes/nanopores internal diameter in 25-110 nm range were developed on surfaces with an initial micro rough topography (Ra = 0.5-2 µm, resulting by CNC turning or by sand blasting and acid etching - SLA). On planar surfaces, the optimal EA process parameters in our custom-built anodization cell are: 0.5 wt.% HF addition in electrolyte, U = 20 V, and Ur = 0.1 V/s - for turned surfaces, and 0.4 wt.% HF addition in electrolyte, U = 24 V, and Ur = 0.08 V/s - for SLA surfaces. For cylindrical surfaces the nanotubes were superimposed on micro rough surface by using 0.4 wt.% HF addition in electrolyte, U = 24 V, and Ur = 0.08 V/s. On threaded surfaces continuous nanoporous oxide layer covering all geometrical features-frontal apex, spiral channels, major diameter, minor diameter, thread flanks - was developed by using 0.4 wt.% HF addition in electrolyte, U = 24 V, Ur = 0.08 V/s, and n = 8 rev/min.

14C release from steels under aerobic conditions

ABSTRACTRadiocarbon (14C) is a key radionuclide in the assessment of the safety of underground geological disposal facilities for radioactive wastes, and the understanding of the 14C behavior in stainless steel may lead to a re-evaluation of the near-surface repository for the disposal of wastes containing this radionuclide in high concentrations. To achieve this objective, leaching experiments were planned for two different scenarios. The first is where the leaching solution, NaOH solution of pH ca. 12 in aerobic conditions, simulates the expected conditions in a cement-based near-surface repository over long time periods. The other one uses an acid solution of 1M H3PO4, which has been proved as a high efficiency chemical removal agent of 14C in graphite. The development of both analytical methods and protocols to measure the release of 14C from the activated steel samples and the speciation in the aqueous and gaseous phase has been undertaken as part of the EC CAST (CArbon-14 Source Term) project. Analytical methods, suitable for identifying and quantifying low molecular weight organic molecules, comprise ion chromatography (IC) and gas chromatography coupled to mass spectrometry (GC-MS); they are described for aqueous and gaseous samples, respectively. In this paper the preparation of leaching experiments to measure the release of 14C and the results obtained are described.

TiO2 nanostructures: voltage influence in corrosion resistance and human osteosarcoma HOS cell responses

Objectives: To develop TiO2 nanostructures using an electrochemical process and evaluate the influence of voltage in the generation of nanotubes and the adhesion of human osteosarcoma cells on anodizing Ti6Al4V surfaces. Methods/ Statistical Analysis: TiO2 nanostructures on Ti6Al4V in a solution of 1M H3 PO4 + 0.2% wt HF for 1 hour at 14 V, 20 V and 25 V were obtained. Surface morphology was evaluated by using scanning electron microscopy and the corrosion behavior of the anodized surfaces was studied using potentiodynamic polarization and Electrochemical Impedance Spectroscopy (EIS). Cell toxicity was evaluated using a colorimetric MTT assay and the cell morphology was reviewed using a fluorescence microscope. Findings: TiO2 nanotubes with diameters of 54.35 nm, 90.84 nm and 85.02 nm were obtained by anodizing at 14 V, 20 V and 25 V respectively. Using an anodizing process an organized and uniform structure was obtained with a density of 130/μm2 , 60/μm2 and 6/μm2 , for the samples anodized at 14 V, 20 V and 25 V respectively. The anodized samples presented nanotubes with intertubular spaces between 10 and 14 nm. The results showed a lower corrosion rate of the anodized surfaces compared to the base material (UT-Ti64), in addition, it was observed that the samples with higher cell count adhered to its surface have higher cell viability percentages, 80% for the samples anodized at 20 V and 25 V. Application/Improvements: The results show that nanostructures could be customized depending on the applications such as higher corrosion resistance and better transport of nutrients favoring the cell metabolism. Keywords: Cell Adhesion, Corrosion Resistance, Nanostructures, TiO2

TiO2 nanostructures: voltage influence in corrosion resistance and human osteosarcoma HOS cell responses

Objectives: To develop TiO2 nanostructures using an electrochemical process and evaluate the influence of voltage in the generation of nanotubes and the adhesion of human osteosarcoma cells on anodizing Ti6Al4V surfaces. Methods/ Statistical Analysis: TiO2 nanostructures on Ti6Al4V in a solution of 1M H3 PO4 + 0.2% wt HF for 1 hour at 14 V, 20 V and 25 V were obtained. Surface morphology was evaluated by using scanning electron microscopy and the corrosion behavior of the anodized surfaces was studied using potentiodynamic polarization and Electrochemical Impedance Spectroscopy (EIS). Cell toxicity was evaluated using a colorimetric MTT assay and the cell morphology was reviewed using a fluorescence microscope. Findings: TiO2 nanotubes with diameters of 54.35 nm, 90.84 nm and 85.02 nm were obtained by anodizing at 14 V, 20 V and 25 V respectively. Using an anodizing process an organized and uniform structure was obtained with a density of 130/μm2 , 60/μm2 and 6/μm2 , for the samples anodized at 14 V, 20 V and 25 V respectively. The anodized samples presented nanotubes with intertubular spaces between 10 and 14 nm. The results showed a lower corrosion rate of the anodized surfaces compared to the base material (UT-Ti64), in addition, it was observed that the samples with higher cell count adhered to its surface have higher cell viability percentages, 80% for the samples anodized at 20 V and 25 V. Application/Improvements: The results show that nanostructures could be customized depending on the applications such as higher corrosion resistance and better transport of nutrients favoring the cell metabolism. Keywords: Cell Adhesion, Corrosion Resistance, Nanostructures, TiO2

Control of Pore Depth in GaN Porous Structures Utilizing a Photoabsorption Process Under below-Bandgap Illumination

Gallium Nitride (GaN) and related materials are attracting much attention as effective materials not only for photo-electronic devices but also for energy conversion devices such as solar cells and photocatalytic devices [1]. We have recently showed that the porous structures formed by the photo-electrochemical (PEC) process are very promising for the energy-conversion devices due to their large surface area and low photo-reflectance properties [2]. However, most of the works on the formation of GaN porous structures have been conducted on the high-doped layer having a carrier density of over 1018 cm-3. In view of the device designing, the decrease of carrier density in the absorption layer is the simplest and the most common method to improve the conversion efficiency since the photo-carries contributing to the photocurrents increased with the depletion layer width. In this study, we investigated the formation of the porous structures in the low-doped n-type GaN layer (5×1016 cm-3) grown on the GaN substrate. From a series of the experimental and theoretical results, we have concluded that the illumination of light with a lower energy than GaN-bandgap is very effective to increase the pore depth in the vertical direction. For the formation of GaN porous structures, the standard electrochemical cell having three electrodes, i.e. a GaN working electrode, a Pt counter electrode and a Ag/AgCl reference electrode, was used with an electrolyte consisting of 1M H2SO4 and 1M H3PO4 solution. A Xe lamp was used for irradiation of monochromatic light whose wavelength was adjusted through a band-path filter. Firstly, the porous structures were formed by the standard PEC process in which an anodic voltage, V a, of 1 V was applied under the front-side-illumination (FSI) with a light wavelength, λ, of 350 nm. Then, the λ was changed to 380 nm corresponding to the photon energy, hv, of 3.26 eV which was below the bandgap energy of GaN (E g = 3.4 eV). From the SEM observation on the GaN surface, the high-density array of pores with a diameter of 40-70 nm and a depth of 250 nm was obtained after the PEC process with λ of 350 nm. However, the pore depth did not increase so much with an etching time. This is because the pore wall thinned to breaking point and was removed from the top-surface by the PEC reactions with photo-carriers generated near the surface [3]. On the other hand, the deeper pores were obtained on the sample formed with λ of 380 nm as compared with the sample formed with λ of 350 nm. Furthermore, the growth rate of pores in depth direction increased with the light power. In order to clarify the obtained results, the anodic currents observed with V a of 10 V and λ of 380 nm were compared between the porous and planar samples. The larger photocurrents were observed in the porous sample even under the transparent light with photon energy below the bandgap. The Frantz-Keldysh (FK) effect is one possible phenomenon to explain the present results. The photons coming from the top-surface penetrated through the GaN but were absorbed by FK effect at the pore tips in which the high-electric field was induced due to the specific sharp structures. In such a situation, the holes are generated only at the pore tips and contribute to the anodization of GaN and pore formation. To clarify the strength of the electric field applied to the GaN porous structures, the potential distribution was calculated by a computer program for solving the 3D Poisson equation. It was clear that a higher electric field was induced at the pore tips and the potential near the surface was more steeply sloped than that of the planar substrate. The result of potential simulation strongly supported the experimental result; namely, the pore depth increased under the illumination of light with λ of 380 nm due to the redshift of the photoabsorption edge arising at the pore tips from the FK effect. This work was supported by JSPS KAKENHI - JP15K13937，JP16H06421，JP17H03224. [1] M. Deguchi et al., Jpn. J. Appl. Phys., 52, 08JF07 (2013). [2] Y. Kumazaki et al., J. Electrochem,. Sci., 161, H705 (2014). [3] A. Watanabe et al., ECS Electrochem. Lett., 4, H11 (2015). Figure 1