Browsing by Author "Muthui, Z. W."

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Density functional study of structural and electronic properties of Ca and Mg doped TiO2
(Journal of Environmental Sustainability Advancement Research, 2022) Mbae, J. K.; Muthui, Z. W.
The scarcity of affordable and environment-friendly sources of energy has led to emergence of photocatalysis to mitigate this problem. This is especially so if the photo catalysts are active in as much a wide region of the solar energy spectrum as possible. Environment-friendly, non-toxic and economical photocatalysts would find application in water treatment, providing another solution to the problem of clean water for domestic use. Of many materials available for photocatalysis is Titanium (IV) oxide (TiO2). It possesses many merits such as low cost, high photocatalytic activity, non-toxicity and high availability. However, drawbacks that limit its application include its optical absorption that falls in the ultraviolet part of the electromagnetic spectrum and rapid electron-hole recombination, which limits its photoquantum efficiency. To extend the optical absorption to a wider region of the solar energy spectrum, various dopants have been added to the oxide. In this study, the effect of doping rutile TiO2 with alkaline earth metals Ca and Mg is investigated using the Density Functional Theory (DFT) method as implemented in the Quantum ESPRESSO simulation package, treating the exchange correlation potential with the Generalised Gradient Approximation. The optimized cell parameters for pure rutile crystal system are 𝑎 = 𝑏 = 4.603Å 𝑐 = 2.992Å, with a volume of 63.393 (Å)3 . On doping there is a slight expansion of the crystal structure and its volume slightly increases by 8.753 (Å) 3 and 28.816 (Å) 3 with Mg and Ca doping respectively. The calculated band gap of undoped rutile is 1.8 eV. Mg and Ca doping raises the valence band edge by 0.2 eV in both Ca and Mg doped rutile. Dopant inter band and intra band states are observed that would be useful in mitigating against charge recombination hence enhancing the efficiency of the photocatalysts. Isolated O 2p states are observed in the Projected Density of States (PDOS) of the doped systems which are normally attributed to enhanced optical absorption of photocatalysts in the visible region. Alkaline earth metal doping of TiO2 rutile modifies the structural and electronic properties of rutile TiO2 in a manner that would make it a more efficient photocatalyst. Co-doping with the alkaline metal dopants could be attempted to investigate the combined effect
“Effect of AC Helmholt magnetic field on the mass of Rosecoco deans”
(Taylor and Francis Online, 2011-06-09) Kamweru, P. K.; Ndiritu, F. G.; Kinyanjui, T. K.; Muthui, Z. W.; Ngumbu, R. G.; Odhiambo, P. M.
Plastic bags mostly made of polyethylene (PE) cause pollution as solid waste due to their non-degradability nature. Initiation of a degradative process by enhanced photo-oxidation is a possible method for an accelerated degradation. This paper presents temperature treatment effects on PE films where photodegradation was initiated using ultraviolet (UV) irradiation in the ranges of 200–300 nm and 300–400 nm for 2 hr. Effects of temperature of 40°C and 55°C on non-UV-irradiated and UV-irradiated PE films processed by conventional methods were investigated and evaluated after 50 hr, 150 hr, and 350 hr of temperature exposure. The effects of UV wavelength range irradiation on the degradation were deduced. Measuring the dynamic moduli using a dynamic mechanical analyzer monitored the degradation. The decrease in average storage modulus was 62% with treatment at 55°C, higher than the 16% drop at 40°C for unirradiated samples after 350-hr exposure. Cross-linking in UV-exposed samples, characterized by an increase in dynamic modulus (stiffening), was observed followed by a reduction of storage modulus. Temperature treatment at 55°C together with 300–400-nm UV range irradiation resulted in the largest increase, i.e., 22% after 150 hr, followed by the largest reduction of storage modulus, i.e., 74.6% for a cumulative 350-hr exposure.
Reflectance, Transmittance and Absorptance of HDPE, LDPE, Glass and Sand Layer Used in a SAH
(2014) Ndegwa, Njoroge G.; Ndiritu, F. G; Hussein, Golicha S. A.; Kamweru, P. K; Kagia, J. K.; Muthui, Z. W.
The total Infra-red (IR) transmission of polymer films is a very important property in engineering, which determines their suitability for a specific application at a given temperature level. Aiming to investigate the percentage IR transmission of two polymer material films and glass of a particular thickness, an analysis is developed for the comparative evaluation of this very important physical property. Sand is a solid and a poor conductor of heat. That means that when sunlight hits sand, all the energy of the sunlight is absorbed in the first millimeter or so of the sand, the heat stays there or spreads only a few millimeters down. So those few millimeters get quite hot. High transmittance and absorptance of top cover and absorber plate are among the factors that contribute to the high efficiency of a SAH. Transmission and reflection spectra were obtained from the Spectro 320 Optical Spectrum Analyzer. IR Radiation (IR) was obtained from a lamp and measurements made at room temperature and relative humidity of 21°C and 25%RH respectively. The study shows that the transmittance of clear HDPE, LDPE and glass are 0.84, 0.72 and 0.72 respectively at wavelengths 791.90, 735 .02 and 820.89nm. The absorptance of sand layers was found to be 56% and 59% for grey and brown sand respectively.
Study of Humidity and UV wavelength effects on degradation of photo irradiated polyethylene films using DMA
(2012-03-12) Kamweru, P. K.; Ndiritu, F. G.; Kinyanjui, T. K.; Muthui, Z. W.; Ngumbu, R. G.; Odhiambo, P. M.
Plastic bags, mostly made of polyethylene, cause pollution as solid waste due to their nondegradable nature. Accelerated degradation, as a solution to mitigate the menace, can be achieved through moisture enhanced photolysis. This study evaluated the effect of three relative humidity environments, i.e., 25%, 40%, and 60% RH, at a constant temperature of 55°C. The effect was studied for ultraviolet (UV) irradiated and nonirradiated samples of polyethylene (PE) films processed under conventional ways. Photodegradation was initiated using ultraviolet irradiation in the ranges (200–300) nm and (300–400) nm for two hours and the effects of subsequent humidity treatment analyzed. Dynamic mechanical analysis was used to measure the dynamic storage modulus to monitor degradation. For nonirradiated samples, there was essentially no change in storage modulus at the three relative humidity environments after 550 hrs. Irradiation in the (300–400) nm range showed faster degradation than for the (200–300)nm range with the highest drop in storage modulus being 67% after 550 hrs. Raising the humidity from 25% to 40% and 60% RH resulted in 41%, 62%, and 67% drop of storage modulus, respectively, at the 550 hrs.
Study of Humidity and UV Wavelength Effects on Degradation of Photo-Irradiated Polyethylene Films Using DMA
(2011-06-09) Kamweru, P. K.; Ndiritu, F. G.; Kinyanjui, T. K.; Muthui, Z. W.; Ngumbu, R. G.; Odhiambo, P. M.
Plastic bags, mostly made of polyethylene, cause pollution as solid waste due to their nondegradable nature. Accelerated degradation, as a solution to mitigate the menace, can be achieved through moisture enhanced photolysis. This study evaluated the effect of three relative humidity environments, i.e., 25%, 40%, and 60% RH, at a constant temperature of 55°C. The effect was studied for ultraviolet (UV) irradiated and nonirradiated samples of polyethylene (PE) films processed under conventional ways. Photodegradation was initiated using ultraviolet irradiation in the ranges (200–300) nm and (300–400) nm for two hours and the effects of subsequent humidity treatment analyzed. Dynamic mechanical analysis was used to measure the dynamic storage modulus to monitor degradation. For nonirradiated samples, there was essentially no change in storage modulus at the three relative humidity environments after 550 hrs. Irradiation in the (300–400) nm range showed faster degradation than for the (200–300)nm range with the highest drop in storage modulus being 67% after 550 hrs. Raising the humidity from 25% to 40% and 60% RH resulted in 41%, 62%, and 67% drop of storage modulus, respectively, at the 550 hrs.
Study of Temperature and UV wavelength Range Effects on degradation of Photo Irradiated polyethylene films using DMA
(2011-06-09) Kamweru, P. K.; Ndiritu, F. G.; Kinyanjui, T. K.; Muthui, Z. W.; Ngumbu, R. G.; Odhiambo, P.M.
Plastic bags mostly made of polyethylene (PE) cause pollution as solid waste due to their non-degradability nature. Initiation of a degradative process by enhanced photo-oxidation is a possible method for an accelerated degradation. This paper presents temperature treatment effects on PE films where photodegradation was initiated using ultraviolet (UV) irradiation in the ranges of 200–300 nm and 300–400 nm for 2 hr. Effects of temperature of 40°C and 55°C on non-UV-irradiated and UV-irradiated PE films processed by conventional methods were investigated and evaluated after 50 hr, 150 hr, and 350 hr of temperature exposure. The effects of UV wavelength range irradiation on the degradation were deduced. Measuring the dynamic moduli using a dynamic mechanical analyzer monitored the degradation. The decrease in average storage modulus was 62% with treatment at 55°C, higher than the 16% drop at 40°C for unirradiated samples after 350-hr exposure. Cross-linking in UV-exposed samples, characterized by an increase in dynamic modulus (stiffening), was observed followed by a reduction of storage modulus. Temperature treatment at 55°C together with 300–400-nm UV range irradiation resulted in the largest increase, i.e., 22% after 150 hr, followed by the largest reduction of storage modulus, i.e., 74.6% for a cumulative 350-hr exposure.