Quantum dots decorated photoanodes in bioelectrochemical fuel cells: Enhanced electricity generation using green algae.

The power performance of the bio-electrochemical fuel cells (BEFCs) depends mainly on the energy harvesting ability of the anode material. The anode materials with low bandgap energy and high electrochemical stability are highly desirable in the BEFCs. To address this issue, a novel anode is designed using indium tin oxide (ITO) modified by chromium oxide quantum dots (CQDs). The CQDs were synthesized using facile and advanced pulsed laser ablation in liquid (PLAL) technique. The combination of ITO and CQDs improved the optical properties of the photoanode by exhibiting a broad range of absorption in the visible to UV region. A systematic study has been performed to optimize the amount of CQDs and green Algae (Alg) film grown using the drop casting method. Chlorophyll (a, b, and total) content of algal cultures (with different concentrations) were optimized to investigate the power generation performance of each cell. The BEFC cell (ITO/Alg10/Cr3//Carbon) with optimized amounts of Alg and CQDs demonstrated enhanced photocurrent generation of 120 mA cm-2 at a photo-generated potential of 24.6 V m-2 . The same device exhibited a maximum power density of 7 W m-2 under continuous light illumination. The device also maintained 98% of its initial performance after 30 repeated cycles of light on-off measurements.

Analysis of heterogeneous gallstones using laser-induced breakdown spectroscopy (LIBS) and wavelength dispersive X-ray fluorescence (WD-XRF).

Laser-induced breakdown spectroscopy (LIBS) is an emerging analytical technique with numerous advantages such as rapidity, multi-elemental analysis, no specific sample preparation requirements, non-destructiveness, and versatility. It has been proven to be a robust elemental analysis tool attracting interest because of being applied to a wide range of materials including biomaterials. In this paper, we have performed spectroscopic studies on gallstones which are heterogeneous in nature using LIBS and wavelength dispersive X-ray fluorescence (WD-XRF) techniques. It has been observed that the presence and relative concentrations of trace elements in different kind of gallstones (cholesterol and pigment gallstones) can easily be determined using LIBS technique. From the experiments carried out on gallstones for trace elemental mapping and detection, it was found that LIBS is a robust tool for such biomedical applications. The stone samples studied in the present paper were classified using the Fourier transform infrared (FTIR) spectroscopy. WD-XRF spectroscopy has been applied for the qualitative and quantitative analysis of major and trace elements present in the gallstone which was compared with the LIBS data. The results obtained in the present paper show interesting prospects for LIBS and WD-XRF to study cholelithiasis better.

Direct spectral analysis and determination of high content of carcinogenic bromine in bread using UV pulsed laser induced breakdown spectroscopy.

Laser induced breakdown spectroscopy (LIBS) was applied for the detection of carcinogenic elements like bromine in four representative brands of loaf bread samples and the measured bromine concentrations were 352, 157, 451, and 311 ppm, using Br I (827.2 nm) atomic transition line as the finger print atomic transition. Our LIBS system is equipped with a pulsed laser of wavelength 266 nm with energy 25 mJ pulse(-1), 8 ns pulse duration, 20 Hz repetition rate, and a gated ICCD camera. The LIBS system was calibrated with the standards of known concentrations in the sample (bread) matrix and such plot is linear in 20-500 ppm range. The capability of our system in terms of limit of detection and relative accuracy with respect to the standard inductively coupled plasma mass spectrometry (ICPMS) technique was evaluated and these values were 5.09 ppm and 0.01-0.05, respectively, which ensures the applicability of our system for Br trace level detection, and LIBS results are in excellent agreement with that of ICPMS results.

Determination of carcinogenic fluorine in cigarettes using pulsed UV laser-induced breakdown spectroscopy.

A spectrometer based on pulsed UV laser-induced breakdown spectroscopy (LIBS) and a highly sensitive intensified charged coupled device camera was developed to determine the carcinogenic substances like fluorine in various brands of cigarettes available commercially. In order to achieve the high sensitivity required for the determination of trace amounts of fluoride in cigarettes and eventually the best limit of detection, the experimental parameters (influence of incident laser energy on LIBS signal intensity and time response of plasma emission) were optimized. In addition, the plasma parameters like electron temperature and electron density were evaluated using Boltzman's plot for cigarette tobacco for the first time. To the best of our knowledge, LIBS has never been applied to determine the fluorine concentration in cigarettes. Along with the detection of fluorine, other trace metals like Ba, Ca, Ni, Cu, and Na were also detected in cigarettes. For determination of the concentration of fluorine, calibration curve was drawn by preparing standard samples in various fluoride concentrations in tobacco matrix. The concentration of fluorine in different cigarette tobacco samples was 234, 317, 341, and 360 ppm respectively, which is considered to be much higher than the safe permissible limits. The limit of detection of our LIBS spectrometer was 14 ppm for fluorine.

Detection of carcinogenic metals in kidney stones using ultraviolet laser-induced breakdown spectroscopy.

The UV single-pulsed (SP) laser-induced breakdown spectroscopy (LIBS) system was developed to detect the carcinogenic metals in human kidney stones extracted through the surgical operation. A neodymium yttrium aluminium garnet laser operating at 266 nm wavelength and 20 Hz repetition rate along with a spectrometer interfaced with an intensified CCD (ICCD) was applied for spectral analysis of kidney stones. The ICCD camera shutter was synchronized with the laser-trigger pulse and the effect of laser energy and delay time on LIBS signal intensity was investigated. The experimental parameters were optimized to obtain the LIBS plasma in local thermodynamic equilibrium. Laser energy was varied from 25 to 50 mJ in order to enhance the LIBS signal intensity and attain the best signal to noise ratio. The parametric dependence studies were important to improve the limit of detection of trace amounts of toxic elements present inside stones. The carcinogenic metals detected in kidney stones were chromium, cadmium, lead, zinc, phosphate, and vanadium. The results achieved from LIBS system were also compared with the inductively coupled plasma-mass spectrometry analysis and the concentration detected with both techniques was in very good agreement. The plasma parameters (electron temperature and density) for SP-LIBS system were also studied and their dependence on incident laser energy and delay time was investigated as well.

Detection of toxic elements using laser-induced breakdown spectroscopy in smokers' and nonsmokers' teeth and investigation of periodontal parameters.

A laser-induced breakdown spectrometer (LIBS) was built and optimized to detect levels of toxic elements such as lead, cadmium, and arsenic present in the roots of extracted teeth of smokers and nonsmokers. Sixty extracted teeth from patients having a history of chronic periodontitis were divided into two groups of 30 teeth each for smoker and nonsmoker patients and, as controls, a third group of 30 patients who did not have a history of chronic periodontitis. The respective elemental concentration (Pb, Cd, and As) 23-29, 0.26-0. 31, and 0.64-11 ppm are for nonsmokers, 35-55, 0.33-0.51, and 0.91-1.5 ppm are for smokers, and lastly 0.17-0.31, 0.01-0.05, and 0.05-0.09 ppm are for control group. In order to test the validity of the results achieved using our LIBS system, a standard inductively coupled plasma (ICP) technique was also applied for the analysis of the same teeth samples, and ICP results were found to be in excellent agreement with our LIBS results. In addition to this, the gingival index, plaque index, clinical attachment loss (CAL) and probing pocket depth were also recorded. Our LIBS spectroscopic analysis showed high levels of lead, cadmium, and arsenic concentration on root surfaces of teeth, which may be due to CAL.

Synthesis, morphology and antifungal activity of nano-particulated amphotericin-B, ketoconazole and thymoquinone against Candida albicans yeasts and Candida biofilm.

In the current study, nano-particulated drugs-Amphotericin-B, Ketoconazole and Thymoquinone (an active ingredient of Nigella sativa)-were prepared using the ball milling technique, and their particle sizes were examined by transmission electron microscopy (TEM) and using a particle size analyzer. The grain sizes of the prepared compounds were found in between 5 to 20 nm, and exhibited quasi-spherical morphology. The antifungal activity of each nano-particulated drug was investigated in vitro against Candida albicans yeasts and Candida biofilm, and compared with their micro-structured conventional forms. Nano-sized drugs were found to be two to four times more effective in disinfecting both the Candida yeasts and Candida biofilm. The study is a first of its kind as nano-forms of drugs have not been studied against Candida and Candida biofilm before. Further investigations are required for the determination of the clinical significance of the nano-formulation of antifungal substances.

Detection of trace elements in nondegradable organic spent clay waste using optimized dual-pulsed laser induced breakdown spectrometer.

The detection of trace elements present in nondegradable organic spent clay waste has been carried out using an optimized dual-pulsed laser induced breakdown spectrometer. The two laser pulses at 1064 and 266 nm were collinearly collimated and focused on the sample surface in order to enhance the signal intensity. The atomic transition lines at 568.8 nm (Na-I), 504.2 nm (Pb-II), 405.8 nm (Pb -I), 443.56 nm (Ca-I), 469.41 nm (S-I), 520.8 nm (Cr-I), 643 nm (Cd-I), and 928.1 nm (Cl-I) were used as marker wavelengths, and the concentrations of 688, 300, 204, 460, and 2440 ppm of Pb, S, Cd, Cr, and Cl, respectively, were detected in the 5% spent clay in the binder. The limits of detection of Pb, S, Cd, Cr, and Cl were estimated to be 6.7, 17.2, 6.5, 5.1, and 14.8 ppm, respectively, from the calibration curve for each element. In order to confirm the reliability of our system, the concentrations of the reported elements detected using our system were compared to the ones obtained with inductively coupled plasma emission spectroscopy and found to be in good agreement.

Nanocatalyst support of laser-induced photocatalytic degradation of MTBE.

This study was undertaken to develop a methodology suitable for the direct removal and degradation of methyl tertiary butyl ether (MTBE) in water using different nano-catalysts supported laser based photo-oxidation process. For this purpose, nano-structured WO3 catalyst was synthesized in our laboratory and its photocatalytic activity for the demineralization of MTBE in water was compared with different catalysts such as ZnO, TiO2, Fe2O3 and NiO using 355 nm laser radiations generated by the third harmonic of Nd: YAG laser. The effect of laser irradiation time, amount of catalysts and pH were also investigated for the optimization of MTBE removal process. For 60 min of laser exposure time, the overall percentage of MTBE degradation was found to be 93%, 89%, 82%, 80% and 71% for WO3, ZnO, Fe2O3, NiO and TiO2, respectively. In addition the photonic efficiencies of different nano-structured catalysts toward degradation of MTBE were estimated, and they were found to follow the trend of WO3 > ZnO > Fe2O3 > NiO > TiO2.

High sensitive detection of nitric oxide using laser induced photoacoustic spectroscopy at 213 nm.

Trace level detection of nitric oxide (NO) is of great interest for a wide range of applications such as environment and human health. For this purpose, a high sensitive sensor based photoacoustic spectroscopy (PAS) principle has been developed at our laboratory for detection of NO at very low concentration (ppbV). For optimization of the PAS signal and to achieve higher sensitivity, parametric dependence investigation was carried out where PAS signal dependence on NO gas pressure, cell geometry, buffer gas (Ar, N2, He), and laser pulse energy used three PAS cells developed locally. The best sensitivity achieved with three cells was 41, 11, 20 ppbv, respectively. It is worth reporting that the best PAS signal to noise ratio was achieved by using a cylindrical cell having three acoustic filters and argon as a buffer gas.

Detection of toxic metals (lead and chromium) in talcum powder using laser induced breakdown spectroscopy.

A laser induced breakdown spectroscopic (LIBS) system was developed using a 266 nm laser and a high-resolution spectrograph (Andor SR 500 i-A) to detect the trace levels of the highly toxic metals such as lead and chromium present in different brands of talcum powder available in the local market. The strongest atomic transition lines of lead (Pb) (405.7 nm) and chromium (Cr) (425.4 nm) were used as spectral markers to simultaneously detect lead and chromium. The LIBS system was calibrated for these two heavy metals, and the system was able to detect 15-20 parts per million (ppm) of lead and 20-30 ppm of chromium in the talcum powder sample. The limits of detection of the LIBS system were also estimated, and they are 1.96 and 1.72 ppm per million respectively for lead and chromium. This study is highly significant due to the use of cosmetic products that could affect the health of millions of people around the globe.

Morphology and antifungal effect of nano-ZnO and nano-Pd-doped nano-ZnO against Aspergillus and Candida.

The present work was aimed to study the activity of nano-particulated ZnO and nano Pd doped nano-ZnO against Aspergillus and Candida species, commonly contaminating the water supply systems. Micro-ZnO was purchased from the market (Aldrich, USA) while nano ZnO were synthesized using sole gel and precipitation methods and their morphology was determined using XRD and TEM techniques. The average grain size of nano-ZnO estimated by these techniques was 30 nm and 20 nm, respectively. The doping of nano-ZnO with 5 % Pd was achieved by a thermal decomposition method and its morphology; as characterized by XRD, TEM and FESEM techniques; gave an average grain size of 35 nm. Serial dilutions of nano-ZnO doped with 5 % Pd, pure nano-ZnO and micro-ZnO (as a control) were prepared from 10 mg/mL stock solution of each in dermasel agar (OXOID), inoculated with standard strains of Candida albicans and Aspergillus niger and incubated at 37°C for 24 and 48 hours, respectively. Their antimicrobial effect was compared by the minimal inhibitory concentration (MIC), determined as the dilution giving a negligible growth of microorganism. Nano-ZnO doped with 5 % nano-Pd, pure nano-ZnO and micro-ZnO, showed antifungal activity against Aspergilus niger with an MIC of 1.25, 2.5 and 5mg/mL, respectively. However, Candida albicans yeasts were relatively resistant to these compounds, with an MIC of 2.5, 5 and 10 mg/mL for Pd doped nano-ZnO, nano-ZnO and micro-ZnO, respectively. Thus nano-ZnO was twice as potent in killing Aspergillus, as compared to its non-nano-counterpart and loading of nano-ZnO with 5 % nano-Pd further increased its activity, four times that of micro-ZnO. Further investigations are needed to confirm the potential use of nano-ZnO and its doping with nano-Pd in the treatment of water supply systems and food preservation.

BiOCl-assisted photodegradation of Rhodamine B under white light and monochromatic green pulsed laser irradiation.

BiOCl-assisted photodegradation of Rhodamine B (Rh. B) molecules was investigated by using white light and green pulsed laser as sources of irradiation in the visible region for the first time. The dependences of removal efficiencies on catalyst dosage, incident pulsed laser energy were investigated and discussed. The dissolved oxygen was found to play an important role during the photochemical reaction. In addition the lowest unoccupied molecular orbital (LUMO) and highest occupied molecular orbital (HOMO) levels of Rh. B molecular were calculated using a Gaussian 03 program. These calculations were valuable to identify the possible photo-catalytic excitation process involved in degradation of Rh.B.

Facile preparation of magnetic C/TiO2/Ni composites and their photocatalytic performance for removal of a dye from water under UV light irradiation.

Development of a photocatalyst with high efficiency and separability is still a challenging task in the field of wastewater treatment. In this study, new magnetic separable C/TiO(2)/Ni composite as a photocatalyst was prepared by a facile pyrolysis reaction, using powdered activated carbon (PAC), TiO(2) and Ni(Ac)(2) as precursors. The results proved that the photocatalyst (C/TiO(2)/Ni) synthesized in this work exhibited greater removal activity for Methyl Orange (MO) dye from water as compared with the commercially available well reported TiO(2) nanoparticles (P25). This significant enhancement in the photocatalytic activity for wastewater treatment due to the combination of PAC and TiO(2) could be presumed as the synergetic effect on the contacting interface of TiO(2) and PAC, and such effect was initially demonstrated by electrochemical impedance measurements. Furthermore, the trait that it consists of magnetic properties and therefore is easy to be recycled, which could be harnessed by an external magnet and may have many advantages over pure metal oxides (like TiO(2)) especially in the industrial procedures.

Pulsed laser-induced photocatalytic reduction of greenhouse gas CO2 into methanol: A value-added hydrocarbon product over SiC.

CO(2) was converted into value-added hydrocarbons (methanol) by laser-induced photocatalytic reduction of CO(2) over commercially available silicon-carbide (SiC) granules as catalyst. The conversion of CO(2) was carried out in a glass reactor having quartz window and equipped with stirring system and was provided with continuous CO(2) flow at ambient conditions. Laser radiations of 355 nm, which were generated by third harmonics of Nd:YAG laser (1060 nm) were applied as an excitation source. The methanol yield as a function of irradiation time and catalysts dosage were monitored by the gas chromatographic analysis (GD-FID) of water samples collected at prescribed intervals. A specific GC column was used which separated hydrocarbons efficiently without any interference from water present in the sample. The study indicated that the commercially available SiC granular material is an excellent catalyst in laser-induced photocatalytic conversion of CO(2) into high value hydrocarbons.

Laser-based photo-oxidative degradation of methyl tertiary-butyl ether (MTBE) using zinc oxide (ZnO) catalyst.

Laser-induced photo-catalytic process for the removal of MTBE from water has been investigated in this study. We have studied the laser-based photo-oxidation of MTBE using ZnO semiconductor catalysts at 355 nm laser radiation generated by third harmonic of Nd: YAG laser. The effect of laser irradiation time, laser energy power, catalyst amount and pH parameters were investigated for the efficient removal of MTBE from water using ZnO catalyst. It was found that at pH value of 8, 300 mg of ZnO catalyst, 60 minutes laser irradiation time and 200 mJ of laser energy, delivered best results with maximum degradation of MTBE in water.

GaN thin films growth and their application in photocatalytic removal of sulforhodamine B from aqueous solution under UV pulsed laser irradiation.

Single-crystalline Gallium Nitride (GaN) thin films were fabricated and grown by metal organic chemical vapor deposition (MOCVD) method on c-plane sapphire substrates and then characterized by high resolution-X-ray diffraction (HR-XRD) and photoluminescence (PL) measurements. The photocatalytic decomposition of Sulforhodamine B (SRB) molecules on GaN thin films was investigated under 355 nm pulsed UV laser irradiation. The results demonstrate that as-grown GaN thin films exhibited efficient degradation of SRB molecules and exhibited an excellent photocatalytic-activity-stability under UV pulsed laser exposure.

Detection of lead in paint samples synthesized locally using-laser-induced breakdown spectroscopy.

A laser-induced breakdown spectroscopy (LIBS) setup was developed to detect lead and other toxic contaminants such as chromium in paint emulsion samples manufactured in Saudi Arabia. The lead concentration detected in these samples was in the 327.2-755.3 ppm range, which is much higher than the safe permissible limit set by Saudi regulatory agencies. Similarly, chromium concentration (98.1-149.5 ppm) was found in high concentrations as well. The results obtained with our LIBS setup are comparable with the sample analysis utilizing a standard technique such as ICP, and our LIBS results are comparable to ICP with in an accuracy limit of 2-4 %.

Facile preparation of magnetic separable powdered-activated-carbon/Ni adsorbent and its application in removal of perfluorooctane sulfonate (PFOS) from aqueous solution.

The main aim of this study was to synthesize magnetic separable Nickel/powdered activated carbon (Ni/PAC) and its application as an adsorbent for removal of PFOS from aqueous solution. In this work, the synthesized adsorbent using simple method was characterized by using X-ray diffractionometer (XRD), surface area and pore size analyzer, vibrating sample magnetometer (VSM), and high resolution transmission electron microscope (HRTEM). The surface area, pore volume and pore size of synthesized PAC was 1521.8 m(2)g(-1), 0.96 cm(3)g(-1), 2.54 nm, respectively. Different kinetic models: the pseudo-first-order model, the pseudo-second-order model, and three adsorption isotherms--Langmuir, Freundlich and Temkin--were applied to study the sorption kinetics and isothermal behavior of PFOS onto the surface of an as-prepared adsorbent. The rate constant using the pseudo-second-order model for removal of 150 ppm PFOS was estimated as 8.82×10(-5) and 1.64×10(-4) for PAC and 40% Ni/PAC, respectively. Our results demonstrated that the composite adsorbents exhibited a clear magnetic hysteretic behavior, indicating the potential practical application in magnetic separation of adsorbents from aqueous solution phase as well.

Design, fabrication, and optimization of photo acoustic gas sensor for the trace level detection of NO2 in the atmosphere.

Photoacoustic (PA) gas sensor for the detection of hazardous NO(2) with detection limit as low as few part per billion by volume (ppbV) has been designed and tested with pulsed UV laser. Some design optimization factors such as the optimum cell geometry, buffer gas etc has been proposed. It was found that a cylindrical cell with many acoustic filters considerably dampens the noise level and also argon as a buffer gas improves the photoacoustic signal level and this combination substantially improved the signal to noise ratio and the limit of detection. Ambiguous decline of photo acoustic signal at higher NO(2) concentration due to the adsorption of NO(2) on the walls of the photoacoustic cells and the dependence of this effect on the buffer gases are also discussed. The PA signal dependence on incident laser energy for three cells was also investigated.