Ylias M. Sabri

Detect, Remove and Reuse: A New Paradigm in Sensing and Removal of Hg (II) from Wastewater via SERS-Active ZnO/Ag Nanoarrays

Mercury being one of the most toxic heavy metals has long been a focus of concern due to its gravest threats to human health and environment. Although multiple methods have been developed to detect and/or remove dissolved mercury, many require complicated procedures and sophisticated equipment. Here, we describe a simple surface enhanced Raman spectroscopy (SERS) active ZnO/Ag nanoarrays that can detect Hg(2+), remove Hg(2+) and can be fully regenerated, not just from Hg(2+) contamination when heat-treated but also from the SERS marker when exposed to UV as a result of the self-cleaning ability of this schottky junction photocatalyst. The sensors are also highly selective because of the unique way mercury (among other chemicals) interacts with Ag nanoparticles, thus reducing its SERS activity.

Controlling Core/Shell Formation of Nanocubic p-Cu2O/n-ZnO Toward Enhanced Photocatalytic Performance

p-Type Cu2O/n-type ZnO core/shell photocatalysts has been demonstrated to be an efficient photocatalyst as a result of their interfacial structure tendency to reduce the recombination rate of photogenerated electron-hole pairs. Monodispersed Cu2O nanocubes were synthesized and functioned as the core, on which ZnO nanoparticles were coated as the shells having varying morphologies. The evenly distributed ZnO decoration as well as assembled nanospheres of ZnO were carried out by changing the molar concentration ratio of Zn/Cu. The results indicate that the photocatalytic performance is initially increased, owing to formation of small ZnO nanoparticles and production of efficient p-n junction heterostructures. However, with increasing Zn concentration, the decorated ZnO nanoparticles tend to form large spherical assemblies resulting in decreased photocatalytic activity due to the interparticle recombination between the agglomerated ZnO nanoparticles. Therefore, photocatalytic activity of Cu2O/ZnO heterostructures can be optimized by controlling the assembly and morphology of the ZnO shell.

Catalytic oxidation and adsorption of elemental mercury over nanostructured CeO2–MnOx catalyst

A nanostructured CeO2–MnOx catalyst was synthesized by a coprecipitation method and subjected to different calcination temperatures at 773 and 1073 K to understand the surface structure and the thermal stability. The structural and redox properties were deeply investigated by various techniques, namely, X-ray diffraction (XRD), inductively coupled plasma-optical emission spectroscopy (ICP-OES), Brunauer–Emmett–Teller (BET) surface area, transmission electron microscopy (TEM), Raman spectroscopy (RS), hydrogen-temperature programmed reduction (H2-TPR), and X-ray photoelectron spectroscopy (XPS). The CeO2–MnOx catalyst calcined at 773 K was tested towards elemental mercury (Hg0) oxidation and the achieved results are compared with the pure CeO2 and MnOx. The XRD and TEM results confirmed the incorporation of Mn ions into the ceria lattice and the formation of a nanostructured solid solution, respectively. The RS and TPR results showed that the CeO2–MnOx catalyst exhibits more oxygen vacancies with superior redox ability over CeO2 and MnOx. XPS analysis indicates that Ce and Mn existed in multiple oxidation states. Compared to pure CeO2 and MnOx, the CeO2–MnOx catalyst exhibited greater Hg0 oxidation efficiency (Eoxi) of 11.7, 33.5, and 89.6% in the presence of HCl, O2, and HCl/O2-mix conditions, respectively. The results clearly indicated that the HCl/O2-mix had a promotional effect on the catalytic Hg0 oxidation. This was most likely due to the presence of surface oxygen species and oxygen vacancies being generated by a synergetic effect between CeO2 and MnOx. In the presence of HCl, the CeO2–MnOx catalyst exhibited good adsorption efficiency (Eads) of 92.4% over pure CeO2 (46.5%) and MnOx (80.6%). It was found that increasing the operating temperature from 423 to 573 K resulted in considerable increase of Eoxi and a decrease in the sorption of Hg0 on the catalyst.

Structural characterization and catalytic evaluation of transition and rare earth metal doped ceria-based solid solutions for elemental mercury oxidation

The catalytic behavior of various CeO2-based solid solutions, namely, Ce1−xTMxO2−δ (TM = Mn, Fe, or Zr) and Ce1−xRExO2−δ (RE = Pr, La, or Sm) was studied for the removal of elemental mercury (Hg0) from coal-derived flue gas by catalytic oxidation (Hg0 → Hg2+). The investigated catalysts were synthesized by a coprecipitation method and characterized by various techniques, namely, X-ray diffraction (XRD), Raman spectroscopy (RS), high-resolution electron microscopy (HREM), Brunauer–Emmett–Teller (BET) surface area, X-ray photoelectron spectroscopy (XPS), temperature programmed reduction (TPR), and diffuse reflectance spectroscopy (UV-DRS). The XRD results confirmed the incorporation of Mn, Fe, Zr, La, Pr, and Sm cations into the CeO2 lattice and the formation of nanocrystalline solid solutions. The TEM measurements established the nanocrystalline nature of the solid solutions. The RS measurements suggested that the substitution process promotes the formation of oxygen vacancies, which hastens the diffusion rate of oxygen and improves the Hg oxidation. UV-vis DRS studies demonstrated the presence of the charge transfer transitions O2− → Ce3+ and O2− → Ce4+. The XPS and H2-TPR results suggested that the reduction of Ce4+ → Ce3+ is the foremost reason for the increase in oxygen vacancies, which are beneficial for Hg0 removal. The order of mercury oxidation activity over various doped catalysts is as follows: CM > CL > CZ > CF > CS > C > CP.

Creating gold nanoprisms directly on quartz crystal microbalance electrodes for mercury vapor sensing

A novel electrochemical route is used to form highly {111}-oriented and size-controlled Au nanoprisms directly onto the electrodes of quartz crystal microbalances (QCMs) which are subsequently used as mercury vapor sensors. The Au nanoprism loaded QCM sensors exhibited excellent response-concentration linearity with a response enhancement of up to ∼ 800% over a non-modified sensor at an operating temperature of 28 °C. The increased surface area and atomic-scale features (step/defect sites) introduced during the growth of nanoprisms are thought to play a significant role in enhancing the sensing properties of the Au nanoprisms toward Hg vapor. The sensors are shown to have excellent Hg sensing capabilities in the concentration range of 0.123-1.27 ppm(v) (1.02-10.55 mg m(-3)), with a detection limit of 2.4 ppb(v) (0.02 mg m(-3)) toward Hg vapor when operating at 28 °C, and 17 ppb(v) (0.15 mg m(-3)) at 89 °C, making them potentially useful for air monitoring applications or for monitoring the efficiency of Hg emission control systems in industries such as mining and waste incineration. The developed sensors exhibited excellent reversible behavior (sensor recovery) within 1 h periods, and crucially were also observed to have high selectivity toward Hg vapor in the presence of ethanol, ammonia and humidity, and excellent long-term stability over a 33 day operating period.

Ceria–zirconia modified MnOx catalysts for gaseous elemental mercury oxidation and adsorption

A series of MnOx/CeO2 (Mn/Ce), MnOx/ZrO2 (Mn/Zr), and MnOx/Ce0.75Zr0.25O2 (Mn/CZ) catalysts prepared by an impregnation method were tested for their ability to catalyse the oxidation of Hg0 at relatively low temperature (423 K). Various characterization techniques, namely, Brunauer–Emmett–Teller (BET) surface area analysis, X-ray diffraction (XRD), Raman spectroscopy (RS), X-ray photoelectron spectroscopy (XPS), and H2-temperature programmed reduction (H2-TPR) were employed to understand the structural, surface, and redox properties of the prepared catalysts. Specific aspects of the catalysis of Hg0 oxidation that were investigated included the influence of MnOx loading (5, 15, and 25%) and the influence of HCl and O2. Among the catalysts tested, the 15Mn/CZ catalyst achieved the best Hg0 oxidation performance (~83% conversion of Hg0 to Hg2+) in the presence of HCl and O2. The higher activity of the 15Mn/CZ catalyst was most likely due to the presence of more oxygen vacancies, enhanced Mn4+/Mn4+ + Mn3+ + Mn2+ ratio and more surface adsorbed oxygen, which were proved by XRD, BET, Raman, and XPS. H2-TPR results also show that the strong interaction between the Ce0.75Zr0.25O2 support and MnOx improved the redox properties significantly as compared to pure CeO2 and ZrO2 supported MnOx catalysts.

Mercury vapor sensor enhancement by nanostructured gold deposited on nickel surfaces using galvanic replacement reactions

Anthropogenic mercury emission is a serious global environmental problem because of its toxicity to humans, plants and wildlife. In order to control these emissions, accurate and reliable online continuous mercury monitoring systems (CMMs) are critical. Such systems can notify appropriate authorities or provide feedback signals to a process control system in time, thus making them an integral part of monitoring and controlling Hg emissions. We demonstrate how nanostructured gold can easily be deposited in small quantities on nickel electrode based QCMs using galvanic replacement (GR) reactions with the resultant surface having excellent Hg monitoring properties. The developed GR surfaces were observed to have higher sensitivity and selectivity in the presence of interfering gas species (NH3 and H2O), as well as to have ∼80% higher mercury sorption capacity than the most efficient mercury sorbents reported to date. Investigations towards the Hg-sensing capabilities of the resultant Ni–Au surface based Hg sensors showed ∼50% better sensitivity and detection limit over control Au films. Furthermore, the GR based QCMs were found to self-regenerate without changing the operating temperature of the sensor, undergoing Hg desorption with sensor recoveries of 93.7–99.3% following Hg exposure at an operating temperature of 90 °C. Surface depth profile analysis of the Ni–Au electrode surfaces showed that the high recovery rate of the sensors was primarily due to the Ni–Au structures, which unlike continuous Au thin-films more commonly used for Hg sensing applications, do not accumulate Hg at the sensitive-layer–substrate interface. Furthermore, the GR Ni–Au surfaces were found to be highly selective towards Hg vapor in the presence of NH3 and H2O interfering gas species which makes them potentially suitable for operating in harsh industrial effluent environments.

Defining the role of humidity in the ambient degradation of few-layer black phosphorus

Few-layer black phosphorus (BP) is an emerging material of interest for applications in electronics. However, lack of ambient stability is hampering its incorporation in practical devices as it demands for an inert operating environment. Here, we study the individual effects of key environmental factors, such as temperature, light and humidity on the deterioration of BP. It is shown that humidity on its own does not cause material degradation. In fact, few-layer BP is employed as a recoverable humidity sensor. This study eliminates humidity as an active parameter in BP degradation. Hence, by simply isolating BP from light, its lifetime can be prolonged even in the presence of O2. As such, this study opens the pathway for devising new strategies for the practical implementation of BP.

Highly efficient nanosized Mn and Fe codoped ceria-based solid solutions for elemental mercury removal at low flue gas temperatures

Ceria (CeO2) is a well-known material for various industrial applications due to its unique redox properties. Such properties, dominated by structural defects that are primarily oxygen vacancies associated with the Ce3+/Ce4+ redox couple, can be easily modulated and optimized by different approaches. In this paper, nanosized Mn and Fe codoped CeO2 solid solutions, Ce0.7−xMn0.3FexO2−δ (x = 0.05–0.2), were prepared by a simple coprecipitation method and tested towards elemental mercury (Hg0) oxidation and adsorption. The obtained solid solutions were characterized in detail at the structural and electronic level by various techniques, namely, XRD, ICP-OES, BET surface area, TEM, Raman, H2-TPR, and XPS. The XRD results suggest that the Mn and/or Fe dopant cations are effectively incorporated into the CeO2 lattice. BET surface area results suggest that the addition of Mn and/or Fe dopants to CeO2 significantly reduces its crystallite size and thereby improves the surface area. Raman, H2-TPR, and XPS results reveal that the Mn and/or Fe dopant cations in the ceria lattice increased the concentration of structural oxygen vacancies and the reducibility of the redox pair Ce4+/Ce3+. The Hg0 oxidation and adsorption studies indicate that Ce0.7−xMn0.3FexO2−δ solid solutions exhibited the highest activity compared to pure CeO2. In particular, the Ce0.5Mn0.3Fe0.2O2−δ (CMF20) solid solution shows an Hg0 oxidation efficiency (Eoxi) of 86.5%. It was found that the doping of both Mn and Fe led to lattice distortion and restrained growth of CeO2, resulting in synergistic increase in oxygen vacancies and catalytic activity.

Nanosphere monolayer on a transducer for enhanced detection of gaseous heavy metal.

This study reports for the first time that polystyrene monodispersed nanosphere monolayer (PS-MNM) based Au (Au-MNM) and Ag (Ag-MNM) nanostructures deposited on quartz crystal microbalance (QCM) transducers can be used for nonoptical based chemical sensing with extremely high sensitivity and selectivity. This was demonstrated by exposing the Au-MNM and Ag-MNM based QCMs to low concentrations of Hg(0) vapor in the presence interferent gas species (i.e., H2O, NH3, volatile organics, etc.) at operating temperatures of 30 and 75 °C. At 30 °C, the Au-MNM and Ag-MNM based QCMs showed ∼16 and ∼20 times higher response magnitude toward Hg(0) vapor concentration of 3.26 mg/m(3) (364 parts per billion by volume (ppbv)) relative to their unmodified control counterparts, respectively. The results indicated that the extremely high sensitivity was not due to the increased surface area (only 4.62 times increase) but due to their long-range interspatial order and high number of surface defect formation which are selectively active toward Hg(0) vapor sorption. The Au-MNM and Ag-MNM also had more than an order of magnitude lower detection limits (<3 ppbv) toward Hg(0) vapor compared to their unmodified control counterparts (>30 ppbv). When the operating temperature was increased from 30 to 75 °C, it was found that the sensors exhibited lower drift, better accuracy, and better selectivity toward Hg(0) vapor but at the compromise of higher detection limits. The high repeatability (84%), accuracy (97%), and stability of Au-MNM in particular make it practical to potentially be used as nonspectroscopic based Hg(0) vapor sensor in many industries either as mercury emission monitoring or as part of a mercury control feedback system.