Q.A. Drmosh

Preparation of a MWCNT/ZnO nanocomposite and its photocatalytic activity for the removal of cyanide from Water using a laser

Nano-zinc oxide (n-ZnO) was loaded onto multi-walled carbon nanotubes (MWCNTs) via a hydrothermal process. Here pure n-ZnO used for loading was synthesized by the pulsed-laser ablation technique while MWCNTs were used as received. The synthesized MWCNT/ZnO nanocomposites were characterized using x-ray diffraction, field emission scanning electron microscopy, high resolution transmission electron microscopy and Fourier transform infrared spectrometry. A model has been proposed for the structural nature of the alignment of ZnO on the surface of MWCNTs. The photocatalytic activity in the removal of highly toxic substances like cyanide (CN) was carried out in a special reactor using pulsed 355 nm UV generated by the third harmonic of an Nd:YAG laser. In order to understand the cyanide removal process, the study was carried out at different laser irradiation times, incident laser energies, pH of the solution and dosage of the MWCNT/ZnO nanocomposite. The study demonstrated that the CN removal process by MWCNT/ZnO composite has higher photocatalytic activity than pure n-ZnO and MWCNTs alone. The mechanism for the degradation using MWCNT/ZnO has been schematically explained. It was noticed that the oxidation process activity is affected by the pH of the solution, and after 20 min of UV laser irradiation, approximately 90% of CN had been degraded.

Synthesis of nanostructured ZnO and ZnO2 by laser ablation process using third harmonic of Nd:YAG laser

A laser-based method was developed for synthesis of nanostructured ZnO/ZnO2 using nanosecond pulsed laser ablation (PLA) on a metallic zinc target in water. Typical laser pulse energy for PLA process was between 40-130 milli-joules per pulse. The addition of an oxidising agent enhanced the nanoparticle yield by 100% and reduced the grain size drastically. A variety of analysis techniques were applied for the characterisation of products. To the best of our knowledge, this is the first time ZnO2 (zinc peroxide) having grain size of 5 nm are produced using laser ablation.

Silver nanoparticles on Zinc Oxide thin film: An insight in fabrication and characterization

In this work, a simple two-steps process has been explained to fabricate silver (Ag) nanoparticles on Zinc Oxide (ZnO) thin film followed by their characterizations. The underneath layer ZnO thin film, as an example, was also investigated how the properties change during the course of nanoparticles fabrication. ZnO thin film was sputtered on standard glass substrate followed by further sputtering of an ultrathin Ag layer. Subsequently the specimen was treated at high temperature in inert environment. A periodic observation at specific temperature intervals confirmed the formation of Ag nanoparticles on ZnO thin film. Field-emission scanning electron microscopic (FESEM) observations revealed the size distribution of as-fabricated Ag nanoparticles in the range of 50-250 nm. Elemental analysis was also confirmed by SEM-aided energy dispersion spectroscopy. The underneath layer ZnO thin film was found to go through recrystallization, stress relaxation, and grain growth during the annealing process. Further treatment to ZnO only film showed a variation in surface topology with reference to those with Ag nanoparticles on ZnO. Such a system was also analysed with finite different time domain (FDTD) analysis. A typical model was considered and FDTD simulation was carried out to understand the trend of absorption depth profile within the absorbing layer involved in plasmonics solar cell.

Growth of metal oxide nanoparticles using pulsed laser ablation technique

Nano particles exhibit physical and chemical properties distinctively different from that of bulk due to high number of surface atoms, surface energy and surface area to volume ratio. Laser is a unique source of radiation and has been applied in the synthesis of nano structured metal oxides. The pulsed laser ablation (PLA) technique in liquid medium has been proven an effective and simple technique for preparing nanoparticles of high purity. Pulsed laser deposition (PLD) is another way to fabricate nano structured single crystal thin films of metal oxides. PLA technique has been applied in our laboratory for the growth of metal oxides such as nano-ZnO, nano-ZnO2 nano- SnO2, nano-Bi2O3, nano-NiO and nano-MnO2. Different techniques such as AFM, UV, FT-IR, PL and XRD were applied to characterize these materials. We will present our latest development in the growth of nano metal oxides using PLA and PLD.

The correlation among morphology, oxygen vacancies and properties of ZnO nanoflowers

Despite numerous reports have investigated the effect of morphology on the properties of nanomaterials, its role in tuning nanomaterials properties is still not clear to date. This work introduces a unique attempt to explore the correlation among morphology, surface defects (oxygen vacancies), and properties of nanomaterials. To achieve this task, three different morphologies of ZnO nanoflowers were prepared via hydrothermal method by varying the concentration of diethylamine. It was observed that a change in ZnO nanoflowers morphology results in changes in their optical, photocatalytic, and antibacterial properties. Photoluminescence and X-ray photoelectron spectroscopy analyses reveal the presence of oxygen vacancies (VO) in ZnO nanoflowers with a concentration varies with respect to morphology. VO concentration plays a key role in tuning ZnO band gap and the concentration of reactive oxygen species and thereby tuning optical, photocatalytic, and antibacterial properties of ZnO nanoflowers. Our results suggest that VO concentration, morphology, and properties of ZnO nanoflowers are correlated.

Direct Z-Scheme Cs2O–Bi2O3–ZnO Heterostructures as Efficient Sunlight-Driven Photocatalysts

Limited light absorption, inefficient electron–hole separation, and unsuitable positions of conduction band bottom and/or valence band top are three major critical issues associated with high-efficiency photocatalytic water treatment. An attempt has been carried out here to address these issues through the synthesis of direct Z-scheme Cs2O–Bi2O3–ZnO heterostructures via a facile, fast, and economic method: solution combustions synthesis. The photocatalytic performances are examined by the 4-chlorophenol degradation test under simulated sunlight irradiation. UV–vis diffuse reflectance spectroscopy analysis, electrochemical impedance test, and the observed transient photocurrent responses prove not only the significant role of Cs2O in extending light absorption to visible and near-infrared regions but also its involvement in charge carrier separation. Radical-trapping experiments verify the direct Z-scheme approach followed by the charge carriers in heterostructured Cs2O–Bi2O3–ZnO photocatalysts. The Z-scheme charge carrier pathway induced by the presence of Cs2O has emerged as the reason behind the efficient charge carrier separation and high photocatalytic activity.

Silver Nanoparticles on Zinc Oxide: An Approach to Plasmonic PV solar cell

Efficient light management in solar cells can be achieved by incorporating plasmonic nanoscatterers that support surface plasmons: excitations of conduction electrons at the interface/surface. As known, light trapping increases the amount of light absorbed by bouncing the light within the cell, giving it a chance to be absorbed thereby increasing the absorption and scattering cross-section. The challenge is to fabricate these plasmonic nanoparticles in cost-effective method as well as without hampering optical, electrical and topographical properties of underneath layers. Here in this report a simple two step method was adopted to fabricate silver nanoparticles on zinc oxide followed by topographic and elemental analysis thereof. Numerical calculation was carried out to elucidate optical scattering of silver nanoparticles of various sizes as well as that of dimer. Near-electric field distribution of single silver nanoparticles and dimer along with the individual component of electric field was simulated by finite different time domain analysis. Using the benefit of increased scattering cross-section and ease of such nanoparticles fabrication, a cell configure is proposed herewith.

Metallic quantum dots as sensitizers for solar cells

The concept of using the metallic quantum dots (MQD) as sensitizer in sensitized solar cells is presented. This concept is only possible due to the nano-scale size effects like emerging energy gap, states redistribution, and phonon bottleneck. Also, the initial work to grow silver quantum dots on ZnO film by sputtering and then post annealing is presented and discussed. This growth procedure will be used later to realize the concept device.