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Thermodynamic, Kinetic and Equilibrium Studies of Pb (II) Ions Adsorption Using Ordinary Clay/Rice Husk Ash Based Geopolymers
(IOSR Journal of Applied Chemistry, 2018-08-08) Maingi, Francis M.; Ng’ang’a, M. M.; Mwangi, H.; Mbuvi, H. M.; Abdulhameed, Adamu
One key global challenge is the existing disparity in water distribution resulting to millions of people lacking access to safe clean water. It is currently assessed that 1.1 billion individuals on the planet lacks access to improved quality water supplies. This is aggravated by the looming climate change and increased pollution threats posed by industrialization and population growth. Use of adsorbents for water treatment is preferable due to simplicity of the technique and cheap materials involved. Geopolymers can be easily synthesized hydrothermally using alumina and silica and possess amorphous surface for use as adsorbents. Clay minerals
have been reported to contain alumina and silica and previous research show that rice husk ash as well contain substantial amounts of silica. Geopolymers can be easily synthesized hydrothermally using alumina and silica and possess amorphous surface that is useful for adsorption. Hence this work reports information on adsorption of Pb (II) using geopolymers GP-1, GP-2 and GP-3 synthesized with SiO2/Al2O3 ratios of 4.16, 4.18 and 8.29 respectively. Adsorption of metal ions was found to increase from 70.54%± 0.43 to 90.23% ± 0.04 with increase in Si/Al ratio from 4.16 to 8.29 in geopolymers. Equilibrium studies unveiled that experimental data for adsorption of Pb (II) ions best fitted in modified Langmuir Freundlich model. The adsorption capacities of 27.0, 79.58 and 209.9mg/g were obtained for GP-1, GP-2 and GP-3 respectively. Adsorption thermodynamics showed the process corresponded on spontaneous physiosorption activated by increase in temperature. Kinetic study on adsorption of Pb (II) ions onto clay based geopolymers was a Pseudo second order. This information may facilitate the development of optimized procedures for wastewater treatment, thus providing an alternative solution to environmental menace caused by heavy metal pollutants.
Biodegradable Superabsorbent Hydrogel from Activated Hydrochar-Glycerol Cross-linked with Maleic Acid
(American Journal of Polymer Science, 2025-08-13) Mukulu, Stanley M.; Mbuvi, Harun M.; Kasimu, Titus M.; Maingi, Francis M.
amounts of water or aqueous solutions due to the presence of hydrophilic functional groups in their network structures. The increasing population, coupled with advanced technologies, has led to a fourfold increase in demand in industrial applications, technological fields, medical fields, and agriculture. This study reports on the synthesis and characterization of superabsorbent hydrogels derived from activated hydrochar. The preparation of hydrochar was done via the dehydration process of sugarcane bagasse, followed by activation using acidified potassium permanganate to form activated hydrochar (AH). The AH was then reacted with glycerol to form polymer units (AHGL). The polymeric units were then reacted with maleic acid to form a superabsorbent hydrogel (SAH). Characterization of the synthesized SAH was carried out using FT-IR, SEM, and XRD. The swelling capacity was optimized by varying contact time and doses of both glycerol and maleic acid. The FT-IR spectra showed a C=O carbonyl spectral absorption peak at 1711.85 cm⁻¹ in SAH, indicating successful crosslinking. The XRD analysis portrayed the amorphous nature of hydrochar and AH, while AHGL and SAH showed semi-crystalline and crystalline nature, respectively. SEM analysis showed dense porous surfaces in SAH compared to rigid surfaces with fewer and unevenly distributed pores in AHGL. The gravimetric technique showed that the maximum absorption capacity of the SAH was obtained at the optimum reaction mole ratio of AH:GL:MA of 10:4:1. The maximum absorption capacity of the synthesized superabsorbent hydrogel relative to its dry mass was found to be 905% and was achieved in a period of 8 hours. Crosslinking the hydrogel improved the water absorption capacity, and hence, it has potential
application in agriculture in arid and semi-arid regions.
Iron uptake in spinach (Spinacia oleracea) using biochar-iron complex derived from sugarcane bagasse under greenhouse conditions
(Journal of Scientific Agriculture, 2025-10-30) Kamaau, Meshack Mutungi; Mbuvi, Harun; Maingi, Francis M.
Iron deficiency limits spinach (Spinacia oleracea) growth and nutritional quality, particularly in alkaline soils. By investigating the complexation of iron with sugarcane bagasse-derived biochar, this study aimed to bridge that gap and offer insights into an innovative approach for improving iron nutrition in spinach crops. This study also evaluated the efficacy of sugarcane bagasse-derived biochar-iron complexes in enhancing iron uptake under controlled greenhouse conditions. Biochar-iron complexes were synthesized via pyrolysis and treated with iron (FeCl3) at 0.25 M, 0.50 M, and 0.75 M. In the greenhouse, using a Randomized Complete Design (RCD), the experiment compared treatments including FeCl3 only, biochar only and biochar-iron complexes at 0.25 M, 0.50 M, and 0.75 M concentrations against an untreated control. Iron uptake in spinach leaves was measured over three months using Atomic Absorption Spectroscopy (AAS). Infrared Fourier Transform Spectroscopy (FT-IR) analysis confirmed key functional groups involved in biochariron chelation, while X-Ray Fluorescence (XRF) revealed increased iron loading, peaking at 0.75 M. Analysis of variance from the greenhouse study revealed significant effects of treatment, time, and their interaction (p<0.001). Although the 0.75 M treatment produced the highest iron content (220 to 300 ppm), the 0.50 M biochar-iron complex is considered optimal, as it achieved iron levels within the FAO guideline range (80-250 ppm). In contrast, conventional FeCl3 treatment-maintained leaf iron at only 1.7-1.9 ppm throughout the three months, reflecting poor soil retention and rapid leaching of FeCl3. These findings highlight the composite’s superior magnitude and temporal stability of iron delivery. Sugarcane bagasse biochar–iron composite thus emerges as a promising, eco-friendly alternative to synthetic iron fertilizers for improving soil fertility and crop nutrition, addressing iron deficiency in sustainable food production.
Synthesis and Characterization of Superabsorbent Hydrogel from Activated Hydrochar-Sucrose Crosslinked with Maleic Acid
(Open Journal of Applied Sciences, 2026-01-30) Mukulu, Stanley M.; Mbuvi, Harun M.; Kasimu, Titus M.; Maingi, Francis M.
Superabsorbent hydrogels are hydrophilic materials forming three-dimensional polymer networks capable of absorbing large amounts of water. They are utilized in various fields, though most current types are non-biodegradable and costly to produce. This research explored a more sustainable approach by synthesizing superabsorbent hydrogels from activated hydrochar derived
from sugarcane bagasse, using acidified potassium manganate for activation and sucrose for polymerization. Maleic acid was employed to create crosslinked structures, optimizing swelling capacity through varying conditions. Characterization through FT-IR confirmed successful crosslinkage. XRD analysis showed the amorphous nature of hydrochar and AH as compared to the increased
crystallinity exhibited by AHSU polymer units and SAH superabsorbent hydrogel. SEM analysis revealed that the superabsorbent hydrogel had compact permeable surface network structures. The optimal synthesis ratio was found to yield a swelling capacity of 778% within 12 hours, highlighting the potential of these biocompatible hydrogels for agricultural applications in semi-arid and
arid regions.
Pyro-processed Coconut Fibre for Removal of Lead Ions from Aqueous Solution
(American Journal of Chemistry and Pharmacy, 2026-05-25) Kasimu, Titus M.; Maingi, Francis M.; Mbuvi, Harun M.; Ng’ang’a, Margaret M.; Abdulhameed, Adamu
Approximately 80% of the population in developing countries lacks access to clean, safe water. A major source of water contamination is heavy metal ions, which pose great risks to human health. This is expected to increase with the projected population and industrial growth if immediate remediation is not taken. Current operational methods for removing the heavy metal ions in wastewater include: chemical coagulation, ion exchange, electrochemical methods, adsorption using activated carbon, natural zeolite, membrane process, ultra-filtration, among others, which are uneconomical due to high costs and unaffordable to low-income
earners. Coconut fibres are locally available agricultural waste that can be converted by activation into adsorbents for water remediation due to their fineness and large surface area. This study reports the synthesis and characterization of coconut fibre charcoal (CFC) and activated coconut fibre charcoal (ACFC) to remediate water contaminated with Pb2+ ions. This involved burning dry coconut fibre in a limited amount of air to obtain coconut fibre charcoal followed by dissolving fine powder of charcoal in 2 M phosphoric acid for 24 hours at a temperature of 25 ºC to obtain activated coconut fibre charcoal. The adsorbents were characterized using FT-IR and SEM. Batch sorption studies were carried out while varying parameters of contact time, shaking speed, temperature, adsorbent dose, pH, and initial concentration of metal ions in solution. Residue Pb2+ ion concentrations were determined using atomic absorption spectroscopy (AAS). The FT-IR results showed absorption peaks at 1423 cm-1 and 840 cm-1 attributed to symmetric –COO- stretch and -OH deformation in ACFC adsorbent, these peaks shifted to 1384 cm-1 and 813 cm-1 while PO4- aromatic strain vibration in ACFC disappeared upon saturation of ACFC with Pb2+ ions respectively. SEM analysis showed pores of different sizes and shapes in ACFC compared to a rigid, concrete, and smooth surface upon saturation with Pb2+ ions. Adsorption data for Pb2+ ions best fitted into the Freundlich model with maximum adsorption capacities of 32.09 mg lead/g activated
coconut fibre charcoal. The results from this study suggest that coconut fibre charcoal and activated coconut fibre charcoal are potential adsorbents of Pb2+ions.