Researcher's Publications

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Browsing Researcher's Publications by Subject "Characterization"

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    Glycerol/lemon juice/based green superabsorbent hydrogel cross-linked with maleic acid
    (2022) Titus M. Kasimu; Harun M. Mbuvi; Francis M. Maingi
    Superabsorbent hydrogels continue to be very important materials due to their applications in several technologies. Unfortunately, most superabsorbent hydrogels currently on the market are acrylate-based products that are non-biodegradable, and, most importantly, some concerns exist about their toxicity for use in agriculture. This study aimed at synthesizing and characterizing biocompatible superabsorbent hydrogel derived from lemon juice. The process involved polymerizing lemon juice (LJ) with glycerol (G) monomers to form polymeric material (HLG-1). HLG-1 was then converted to HLG-2 by crosslinking with maleic acid. Characterization of the hydrogels was done using Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscope (SEM), and X-ray diffraction (XRD). The synthesis conditions producing optimal swelling capacity were studied by varying contact time and dosage of both lemon juice and the cross-linker. The FT-IR results showed a peak at 1528 cm-1 and 1591.34 cm-1 associated with –COO- stretching indicating successful polymerization and crosslinking processes. XRD analysis showed conversion from amorphous to crystalline phases upon crosslinking. SEM micrographs showed clear pores with large surface area in HLG-2 compared with the rigid and constricted surface of HLG-1 hydrogel. A maximum swelling capacity of 910% was obtained upon synthesizing hydrogel HLG-2 with lemon juice, glycerol, and maleic acid of a volume ratio of 5.4: 3.75: 3.75 respectively. Crosslinking the hydrogel with maleic acid was found to improve the water absorption capacity of the hydrogel. The superabsorbent hydrogel with such high swelling and water absorption ability has the potential of being applied in arid and semi-arid regions to boost agricultural production.
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    Long Term Characterization of Dust and Its Radiative Forcing over Kenya Using Satellite and Model-Based Data
    (Atmospheric and Climate Sciences, 2025-09-02) Simiyu, Kizito W.; Khamala, Geoffrey W.; Makokha, John Wanjala
    Dust aerosols play a critical role in atmospheric processes, influencing air quality, climate, and weather patterns through their interactions with radiation and cloud formation. This study aimed at characterizing the spatiotemporal distribution of dust and quantifying its radiative forcing over Kenya using a combination of satellite observations and model-based measurements. Multi-year datasets from MERRA-2 and MODIS were utilized to analyze dust loading and spatial variability. Additionally, radiative forcing (RF) derived from MERRA-2 and satellite observations was estimated to assess dust-induced changes in surface of-atmosphere (BOA), top-of-atmosphere (TOA) and within atmosphere (ATM). The findings on spatiotemporal variability of dust over Kenya, highlight high concentrations in northern regions during dry months and reductions during wet seasons (MAM and OND). While on particle size distribution, the analysis shows coarse-mode dominance in dry periods, depicting dominance of dust. On the other hand, dust mass concentrations peak in the northwest part of the study domain. Further, RF analysis indicates dust induces BOA and TOA cooling but atmospheric heating, with peak heating in June to July, local dry months. This study therefore recommends an enhanced integrated dust monitoring and modeling system, especially during dry seasons, to capture Dust AOD, size, and mass concentration. Further, targeted mitigation measures like afforestation, land-use planning and early warning systems should be prioritized to reduce dust emissions, improve climate model accuracy, and protect public health in vulnerable regions.
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    Super Absorbent Hydrogel Derived from Activated Charcoal Functionalized with Ethylenediamine and Cross-linked with Maleic Acid
    (International Journal of Materials and Chemistry, 2022-01-13) Titus M. Kasimu; Harun M. Mbuvi; Francis M. Maingi
    Superabsorbent hydrogels represent a set of polymeric materials with three-dimensional networks capable of holding a huge amount of water due to their hydrophilic nature in their structure. Their application in industries and the environment is of prime importance. This study reports the synthesis and characterization of superabsorbent hydrogels derived from activated charcoal. The activated charcoal (AC) was functionalized with ethylenediamine (EA) using sodium hydroxide as a catalyst in the absence and presence of maleic acid as a cross linker to synthesize HCE-1 and HCE-2 superabsorbent hydrogel respectively. Characterization of the hydrogels was done using Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscope (SEM), and X-ray diffraction (XRD). The synthesis conditions producing optimal swelling capacity were studied by varying contact time and dosage of both activated carbon and the maleic acid. The results showed presence of C-N- stretching vibration at 1590.99 cm-1 in FT-IR spectrum of HCE-1 indicating interlinking between AC and EA monomers. XRD analysis showed a shift from amorphous to crystalline upon crosslinking. SEM analysis showed dense mast homogenous morphology with clear pores network in HCE-2 compared to the rigid rough surface observed in HCE-1 hydrogel. The dose ratio of AC: EA: maleic acid of 6:5:2 produced hydrogel with highest water absorption capacity of 1089.7±0.6%. Crosslinking the hydrogel with maleic acid was found to improve the water absorption capacity of the absorbent. The study provides a baseline for the application of the hydrogel in agriculture, especially in semi and arid regions.
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    Superabsorbent Hydrogel derived from Lemon Juice/Ethylenediamine with Maleic Acid as a Cross-Linker
    (International Journal of Composite Materials, 2021-10-30) Titus M. Kasimu; Harun M. Mbuvi; Francis M. Maingi
    Hydrogels are 3-dimensional polymer network materials with the ability to absorb a large amount of water. The current advancement in technology has increased their demand in the fields of industrial and environmental applications. This study reports the synthesis and characterization of superabsorbent hydrogels derived from lemon juice. The preparation involved linking lemon juice (LJ) with Ethylenediamine (EDA) via an amide linkage to obtain HLE-1 hydrogel. The polymer hydrogel was then cross-linked with maleic acid via an ester linkage to form HLE-2 hydrogel. Characterization was done using FT-IR, SEM, and XRD. The optimization of the swelling conditions was studied by varying contact time and the dosage of both lemon juice and the cross-linker. XRD analysis showed the conversion of amorphous hydrogel HLE-1 to crystalline hydrogel HLE-2 upon cross-linking. The FT-IR spectra showed a new strong symmetric stretching -COO- peak at 1079.83 cm-1 in HLE-2 indicating successful ester linkage. SEM analysis showed pores of different sizes and shapes in HAE-2 compared to a rigid, concrete, and smooth surface in HLE-1. Upon the optimization of the synthesis conditions of the cross-linked hydrogel, a swelling capacity of 925% was obtained. Crosslinking the hydrogel improved its water absorption ability. The high swelling capacity of the hydrogel provides a baseline for potential application in agriculture, especially in semi and arid regions.
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    Synthesis And Characterization Of Struvite By Aqueous Precipitation Using Wastewater And Hot Spring Water
    (IOSR Journal of Applied Chemistry, 2024-07-22) Nasambu, Edith; Maingi, Francis; Ouma, Linda Immaculate
    Struvite (MgNH4PO4.6H2O) is a phosphate mineral that has recently become a prudent venture for many researchers due to its nutritional value to plants in the field of agriculture. The cost of production of this mineral heavily relies on the cost of the magnesium source used. In this study, hot spring water was investigated as a potentially cheaper natural source of magnesium ions while sewage wastewater was used as a source of phosphate and ammonium ions for the struvite synthesis. The synthesized struvite composite was then characterized using X-ray fluorescence (XRF), X-ray diffraction (XRD), and Scanning electron microscope (SEM). The precipitate purity and phosphorous recovery were analysed. XRF results showed that synthesized struvite majorly consisted of magnesium oxide and phosphorous oxide. XRD analysis showed the presence of orthorhombic crystalline phases between 4-9 degrees (2𝜃) with struvite peaks at 2𝜃 values 15.8, 20.9and 46.3 which matched struvite ICDD card information. SEM revealed irregular, crystalline, and rod-like morphological structures that were consistent with those identified in the literature. The synthesized composite contained a percentage purity of 68.61% and phosphorous recovery of 76.15%. The presence of phosphorous and nitrogen in the struvite which is plant macronutrients makes the composite potential fertilizer for agricultural applications.