Silver Anchored Polyaniline@Molybdenum Disulfide Nanocomposite (Ag/Pani@MoS2) for Highly Efficient Ammonia and Methanol Sensing under Ambient Conditions: A Mechanistic Approach

We report the synthesis of silver anchored and para toluene sulfonic acid (pTSA) doped polyaniline/molybdenum disulfide nanocomposite (pTSA/Ag-Pani@MoS2) for highly reproducible room temperature detection of ammonia and methanol. Pani@MoS2 was synthesized by in situ polymerization of aniline in the presence of MoS2 nanosheets. The chemical reduction of AgNO3 in the presence of Pani@MoS2 led to the anchoring of Ag to Pani@MoS2 and finally doping with pTSA produced highly conductive pTSA/Ag-Pani@MoS2. Morphological analysis showed Pani-coated MoS2 along with the observation of Ag spheres and tubes well anchored to the surface. Structural characterization by X-ray diffraction and X-ray photon spectroscopy showed peaks corresponding to Pani, MoS2, and Ag. The DC electrical conductivity of annealed Pani was 11.2 and it increased to 14.4 in Pani@MoS2 and finally to 16.1 S/cm with the loading of Ag. The high conductivity of ternary pTSA/Ag-Pani@MoS2 is due to Pani and MoS2 π–π* interactions, conductive Ag, as well as the anionic dopant. The pTSA/Ag-Pani@MoS2 also showed better cyclic and isothermal electrical conductivity retention than Pani and Pani@MoS2, owing to the higher conductivity and stability of its constituents. The ammonia and methanol sensing response of pTSA/Ag-Pani@MoS2 showed better sensitivity and reproducibility than Pani@MoS2 owing to the higher conductivity and surface area of the former. Finally, a sensing mechanism involving chemisorption/desorption and electrical compensation is proposed.</jats:p

Spatial and temporal distribution of heavy metals in coastal core sediments from the Red Sea, Saudi Arabia

Jeddah is the most industrialized city on the west coast of Saudi Arabia and is under increasing influence of human activities. Heavy metals data were obtained from four near-coast Red Sea sediment cores in close proximity to Jeddah. Chromium, manganese, iron, copper, zinc, and lead were analyzed from depth-resolved sections of each core via heavy acid digestion and inductively coupled plasma-mass spectrometry (ICP-MS). The average concentrations of all four sites were 245.96 mg kg1, 478.45 mg kg1, 8506.13 mg kg1, 251.82 mg kg1, 623.09 mg kg1, and 362.75 mg kg1, respectively. The depth-resolved results showed that highest concentrations of Mn, Cu, and Pb were found in the top 15 cm of the core profile distributions compared to other depth sub-samples. Heavy metal concentrations in core sediments are increased near central Jeddah and have become higher in recent years. The results of enrichment factor calculations indicate little anthropogenic supply of Mn and Cr while Pb, Zn, and Cu show strong anthropogenic input. The Pollution Load Index was higher in the two sites closer to central Jeddah where power and desalination plants and wastewater release are known. This indicates that the area has suffered from heavy metal pollution compared to other non-industrialized sites in the Red Sea. Heavy metal contaminations due to anthropogenic activity should be taken into account to protect the Red Sea during future growth. The results of this work should be considered as a baseline for heavy metals monitoring in the sediments of the Red Sea coast near Jeddah, Saudi Arabia