Asmah Hj Yahaya

Controlled release of a plant growth regulator, α-naphthaleneacetate from the lamella of Zn–Al-layered double hydroxide nanocomposite

Formation of the so-called organic-inorganic nanohybrid material was exploited for the preparation of a controlled release formulation. The inorganic Zn-Al-layered double hydroxide (LDH) was used as a matrix, hosting an active agent or a guest, alpha-naphthaleneacetate (NAA), a plant growth regulator by self-assembly technique. The reverse process, i.e., the deintercalation or release of the guest, NAA was found to be rapid initially, followed by a more sustained release thereafter and this behavior was dependent on the pH of the release medium, the aqueous solution. The mechanism of release has been interpreted on the basis of the ion-exchange process between the NAA anion intercalated in the lamella host and nitrate or hydroxyl anions in the aqueous solution.

Nanocomposite-based controlled release formulation of an herbicide, 2,4-dichlorophenoxyacetate incapsulated in zinc–aluminium-layered double hydroxide

Abstract Controlled release formulation of an herbicide, 2,4-dichlorophenoxyacetate (24D) was developed by the virtue of the formation of organic–inorganic nanohybrid material and its ion exchange property. The inorganic Zn–Al layered double hydroxide (ZAL) was used as a matrix, hosting an active agent or a guest, 24D by self-assembly technique. The resulting material (ZAD) was subsequently used to study the release property of 24D into aqueous solutions containing chloride, carbonate as well as distilled water. The release of the guest 24D was found to be rapid initially followed by a more sustained release thereafter and this behavior was dependent on the type of anions and their concentrations in the release medium, the aqueous solution. The mechanism of release has been interpreted on the basis of the ion exchange process between the 24D anion intercalated into the interlamellae host and carbonate or chloride and/or hydroxyl anions in the aqueous solution.

Chemical composition and antioxidant activity of Strobilanthes crispus leaf extract

This study investigated the components present in and the total antioxidant activity of leaves of Strobilanthes crispus (L.) Bremek or Saricocalyx crispus (L.) Bremek (Acanthacea). Proximate analyses and total antioxidant activity using ferric thiocyanate and thiobarbituric acid methods were employed. Minerals content was determined using the atomic absorption spectrophotometer, whereas the water-soluble vitamins were determined by means of the UV-VIS spectrophotometer (vitamin C) and fluorimeter (vitamins B(1) and B(2)). Catechin, tannin, caffeine, and alkaloid contents were also studied. All data were compared to the previously reported results of Yerbamate, green tea, black tea, and Indian tea. The dried leaves contained a high amount of total ash (21.6%) as a result of a high amount of minerals including potassium (51%), calcium (24%), sodium (13%), iron (1%), and phosphorus (1%). High content of water-soluble vitamins (C, B(1), and B(2)) contributed to the high antioxidant activity of the leaves. The leaves also contained a moderate amount of other proximate composition as well as other compounds such as catechins, alkaloids, caffeine, and tannin, contributing further to the total antioxidant activity. Catechins of Strobilanthes crispus leaves showed highest antioxidant activity when compared to Yerbamate and vitamin E. Consumption of the leafy extract daily (5 g/day) as an herbal tea could contribute to the additional nutrients and antioxidants needed in the body to enhance the defense system, especially toward the incidence of degenerative diseases.

Synthesis of layered organic–inorganic nanohybrid material: an organic dye, naphthol blue black in magnesium–aluminum layered double hydroxide inorganic lamella

Open lamella systems such as layered double hydroxides (LDHs) can be used to generate new nanostructured materials of layered organic–inorganic nanohybrid type. The synthesis of a new nanocomposite material consisting of inorganic layers, Mg–Al-LDH (MAL) as a host and naphthol blue black (NBB), an organic dye as a guest was successfully done. Various concentrations of NBB, ranging from 0.001 to 0.0015 M were used to prepare the nanocomposite under different Mg/Al molar ratios and pH. The concentration of NBB of 0.0015 M at pH 10 was found to be able to give a well-ordered nanolayered organic–inorganic hybrid structure with basal spacing of 19.6 A.

Oil Palm Trunk as a Raw Material for Activated Carbon Production

Oil palm trunk is a major lignocellulosic-rich, solid waste material generated from palm-oil upstream industry. The activated carbons prepared from oil palm trunk pretreated with phosphoric acid with the ratio of the acid to the precursor of 0.9, followed by carbonization and activation by carbon dioxide resulted in a high surface area of more than 1800 m2/g with 90% content of micropore surface area. The surface area and the nature of the porosity of the resulting activated carbons were found to be dependent on the amount of the activator used for a fixed quantity of the precursor. Pretreatment of the precursor at low ratio of the phosphoric acid has added advantage, due to the tremendous increase in the apparent surface area of the resulting activated carbon and at the same time enriching its micropore nature. This could result in the conservation of the micropore fraction. On the other hand, using too high a ratio of the phosphoric acid to the precursor did not increase the apparent surface area very much, but instead destroyed the micropore component, and thus increasing the mesopore fraction of the resulting activated carbon. This study also shows that oil palm trunk, a by-product of oil palm industry has a great potential as a raw material for activated carbon production.

Bacillus cereus as a biotemplating agent for the synthesis of zinc oxide with raspberry- and plate-like structures

Currently the development of green chemistry approach with the use of biomaterial-based activities of microbial cells in the synthesis of various nanostructures has attracted a great attention. In this study, we report on the use of bacterium, Bacillus cereus as a biotemplating agent for the formation of zinc oxide nanoparticles with raspberry- and plate-like structures through a simple thermal decomposition of zinc acetate by maintaining the original pH of the reaction mixtures. Possible mechanism on the formation of the nanostructures is proposed based on the surface chemistry and biochemistry processes involved organic-inorganic interactions between zinc oxide and the microbial cells.

Effect of incoming and outgoing exchangeable anions on the release kinetics of phenoxyherbicides nanohybrids

The release of chlorophenoxyherbicides agrochemicals, namely 2-chloro- (2CPA), 4-chloro and 2,4,5-trichloro (TCPA) phenoxyacetates from their nanohybrids into various aqueous solutions; carbonate, sulfate and chloride was found to be controlled by pseudo-second order rate expression. The percentage saturated released was found to be anionic-dependent, in the order of carbonate>sulfate>chloride for the release media and 2CPA>4CPA>TCPA for the anionic guests. This study demonstrates that the release of the phenoxyherbicides agrochemicals from the nanohybrid compounds can be tuned by choosing the right combination of exchangeable anions both the incoming and the outgoing anions.

Acid fuchsin-interleaved Mg–Al-layered double hydroxide for the formation of an organic–inorganic hybrid nanocomposite

Abstract Layered organic–inorganic hybrid nanocomposite, containing an organic dye in an inorganic interlayer was prepared using acid fuchsin (AF) as a guest in Mg–Al layered double hydroxide inorganic host by a self-assembly technique, with the Mg–Al ratio in the mother liquor of 4 and pH=7.5. Powder X-ray diffractogram shows that the basal spacing of the Mg–Al layered double hydroxide with nitrate as the intergallery anion expanded from 8.9 to 17.1 A to accommodate the AF anion, for the formation of the Mg–Al layered double hydroxide-AF layered organic–inorganic hybrid nanocomposite (MAAF). Formation of such a material is useful for example for coating or controlled release purposes of dye for slow dyeing process.

The Effect of Single, Binary and Ternary Anions of Chloride, Carbonate and Phosphate on the Release of 2,4-Dichlorophenoxyacetate Intercalated into the Zn–Al-layered Double Hydroxide Nanohybrid

Intercalation of beneficial anion into inorganic host has lead to an opportunity to synthesize various combinations of new organic–inorganic nanohybrids with various potential applications; especially, for the controlled release formulation and storage purposes. Investigation on the release behavior of 2,4-dichlorophenoxyacetate (2,4-D) intercalated into the interlayer of Zn–Al-layered double hydroxide (ZAN) have been carried out using single, binary and ternary aqueous systems of chloride, carbonate and phosphate. The release behavior of the active agent 2,4-D from its double-layered hydroxide nanohybrid ZANDI was found to be of controlled manner governed by pseudo-second order kinetics. It was found that carbonate medium yielded the highest accumulated release of 2,4-D, while phosphate in combination with carbonate and/or nitrate speeds up the release rate of 2,4-D. These results indicate that it is possible to design and develop new delivery system of latex stimulant compound with controlled release property based on 2,4-D that is known as a substance to increase latex production of rubber tree,Hevea brasiliensis.

Synthesis of Phenoxyherbicides-Intercalated Layered Double Hydroxide Nanohybrids and Their Controlled Release Property

Synthesis of new generation of agrochemicals of phenoxyherbicides-type, namely 2-chloro- (2CPA) and 2,4,5- trichlorophenoxy acetates (TCPA) were accomplished by hybridization of the phenoxyherbicides into zinc-aluminium-layered double hydroxide interlamellae for the formation of new nanohybrids of 2CPA and TCPA, labeled as N2CPA and NTCPA, respectively. Basal spacing expansion from 8.9 A in the layered double hydroxide (LDH) to 18.5 and 26.2 A in the resulting N2CPA and NTCPA nanohybrid, respectively, together with FTIR, CHNS and TGA/DTG data support that the phenoxyherbicides were successfully intercalated into the layered double hydroxide inorganic interlayers. The release of the phenoxyherbicides from their nanohybrids at various pHs can be expressed by parabolic diffusion at the beginning of the process, but the release data for the whole process followed the pseudo-second order equation. The release process was found to be pH-dependent, in the order of pH 12 > 3 > 6.25. In addition, the release time for TCPA is longer than 2CPA, suggesting a stronger interaction of TCPA than 2CPA with the layered double hydroxide inorganic interlayer. This study indicates the potential application of zinc-aluminium-layered double hydroxide as the matrix of the controlled release formulation of agrochemicals such as 2-chlorophenoxyacetic acid and 2,4,5-trichlorophenoxyacetic acid.