Maxwell Obumba^1, Naumih Noah^2* and Mildred Nawiri¹

¹Chemistry Department, Kenyatta University, P.O Box 43844-00100, Nairobi
²School of Pharmacy and Health Sciences, United States International University-Africa, P.O Box 14634-00800, Nairobi  

Abstract

Metal nanoparticles have been studied for their unique physical and chemical properties which make them efficient in various models and applications. Specifically, Silver nanoparticles (AgNPs) and Gold nanoparticles (AuNPs) have recognizable importance in chemistry, physics and biology because of their unique electrical, photothermal and optical properties. The size, surface chemistry, dispersion media and shape of AgNPs and AuNPs have a profound impact on their properties. The need to synthesize AgNPs and AuNPs with a predetermined size, shape and fair stability has been growing over the past and present decades. Several methods have been developed in the recent past, they include; chemical reduction, photochemical reduction, radio-lytic methods and electrochemical techniques. Most of these methods have shown success in the synthesis of AgNPs and AuNPs but their potential to provide smaller particle sizes and prevent agglomeration is still a major drawback. The use of polymeric materials as reducing agents and stabilizers is a promising method for obtaining monodispersed AgNPs and AuNPs with desirable stability. The current study demonstrates the feasibility of synthesizing small-sized AgNPs and AuNPs with better stability using nanostructured polyamic acid (PAA) as both reducing and stabilizing agent under the condition of room temperature. Polyamic acids are a class of polymer formed through polycondensation reactions between a dianhydride and a diamine. The amine and anhydride groups react to form carboxylic acid groups which release electrons in the reaction thereby reducing silver and gold ions. The carboxylic acid groups then encapsulate the newly formed AgNPs and AuNPs stopping their further growth and hence preventing them from agglomeration. Studies using UVVis spectrometry showed absorption spectra that correspond to the peaks of silver and gold nanoparticles. The bands in the region of 425nm to 433nm confirmed peaks for AgNPs while 533nm to 541nm confirmed peaks for AuNPs. The Mie’s equation depicted estimated particle sizes ranging between 26nm to 32nm and 24nm to 30nm for AgNPs and AuNPs respectively. The Surface Plasmon Resonance (SPR) bands remained unchanged over a period of beyond three months depicting better stability of the silver and gold nanoparticles. Therefore, it can be correctly concluded that PAA is a prominent reducing and stabilizing agent in the synthesis of stable AgNPs and AuNPs.

Keywords: Agglomeration, silver and gold nanoparticles, Polyamic acid, stability

Obumba et al. JKCS 16-1 (2023) 20-24

Lorna C. Chesir*, Peter O. Ongoma*

Department of Chemistry, Egerton University, P.O. Box 536-20115, Egerton, Kenya 

Abstract

Understanding the association of organic matter and minerals in petroleum source rocks is a vital component of the hydrocarbongeneration process, especially in unconventional reservoirs, which are the targets of hydrocarbon exploration today. In this study, five source rock samples selected from three wells namely, Chalbi-3, Sirius-1, and Ndovu-1wells from the Anza basin, were investigated to characterise the thermal decomposition process using differential scanning calorimetry (DSC) and thermogravimetry (TG/DTG) with a heating rate of 10 °C min−1 in an oxidizing atmosphere. The Anza basin is a sedimentary basin located in the north-eastern part of Kenya. The source rocks displayed variable degrees of organic richness, with TOC contents ranging from 0.54 to 1.99 wt. %, at subsurface depths ranging from 1067–3100 m. The Ndovu-1 (H) sample had the highest TOC value, while Sirius-1 (F) had the lowest. In all the analyses, the TG/DSC curves allowed three distinct decomposition regions of organic matter and inorganic matter decomposition identified as i) low-temperature oxidation of bitumen (temperature ranging from 257 °C to 350 ° C), ii) thermooxidation of the kerogen (between 430 and 560 °C), and iii) high-temperature decomposition of calcite mineral (between 723 and 747 °C), and clay minerals in the temperature range 907 and 923 °C. There was also a strong correlation between the mass loss and combustion of organic matter in the source rocks

Keywords:

source rocks, TG/DTG/DSC analysis, Thermo-oxidative decomposition, Anza basin

Chesir, L.C & Ongoma, P.O. JKCS 16-1 (2023), 13-19

George O. Okonji^{*1, 3,} Dickson Andala¹ and Silvanus Shisia² 

¹Department of Chemistry, Multimedia University of Kenya, P.O.BOX 15653-00503, Nairobi, Kenya
²Department of Chemistry and Biochemistry, Laikipia University, P.O.BOX 1100-20300, Nyahururu, Kenya
³School of Chemistry and Material Science, Technical University of Kenya, P.O.BOX 52428-00200, Nairobi, Kenya 

Abstract

Prenatal and postnatal exposure to endocrine disrupting pesticides (EDPs) is believed to cause hormonal imbalance in animals. Insufficient data on exposure levels has necessitated the need for assessments to confirm existing EDPs. Solid phase extraction (SPE) is a simple multi-residue sample preparation technique suitable for quick exposure assessments; however, extension of its application in pre-concentration of many EDPs residues in river water is largely unexplored. The method was applied in analysis of Mbagathi River water samples in Machakos County, Kenya. This study aimed to validate a SPE technique for pre-concentration of four suspected EDPs including a triazine (atrazine), a carbamate (carbaryl) and organophosphates (diazinon and dimethoate) in river water for direct liquid chromatography tandem mass spectrometric (LC-MS/MS) analysis. Precision attained was less than 2.6% RSD, while recovery was above 70% for majority of the compounds tested. Low limits of quantification and detection, below 2.5 ng/L and 0.8 ng/L respectively, indicated suitability of the method for trace exposure assessment in river waters. Samples were collected in triplicate from eighteen sampling sites at random along the river during the short rainfall season of mid-September 2019. The selected EDPs detected were in the range of: <LOQ to 3.56 μg/L for atrazine, <LOQ to 1.48 μg/L for carbaryl, <LOQ to 1.9 μg/L for diazinon and <LOQ to 0.82 μg/L for dimethoate. The quantities detected for atrazine, carbaryl, dimethoate and diazinon in a majority of sites were at levels capable of causing significant health effects to human and wildlife.

Keywords: River water, Endocrine Disrupting Pesticides, Liquid chromatography, Solid Phase Extraction, Tandem mass spectrometry  

Okonji et al. JKCS 16-1 (2023) 1-12