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The purpose of this research is to investigate biosorption characteristics of two cationic dyes, methylene blue (MB) and methyl violet 2B (MV), on breadfruit (Artocarpus altilis) peel and core. Characterization of breadfruit waste was conducted using surface titrations, thermogravimetry, and Fourier transform infrared spectroscopy. The extent of interaction between dyes and each biosorbent was monitored by absorbance measurements, which was then used in isotherm, thermodynamics, and kinetics analysis. Biosorption of MB and MV on breadfruit peel and core reaches equilibrium in 150–180 min. All four systems under investigation (MB-breadfruit peel, MB-breadfruit core, MV-breadfruit peel, and MV-breadfruit core) show similar extent of dye removal of about 80% under the conditions employed. Biosorption of both dyes on both biosorbents follow the Langmuir adsorption isotherm model at the ambient pH, at which the breadfruit surface bears a negative charge. Kinetics of biosorption of MB on breadfruit waste is so fast that it is not possible to determine the order of adsorption kinetics at the concentration level employed. The rate of biosorption of MV on breadfruit waste is smaller and follows pseudo second order kinetics with rate constants of 153.5 and 31.7 g mmol−1 min−1 for peel and core, respectively. Thermodynamics studies conducted for each biosorption system provide negative ΔG Θ, ΔH Θ and ΔS Θ values with the maximum biosorption for MB at the ambient temperature of 24 °C, while that for MV is obtained between 40 and 50 °C. All four biosorption systems show spontaneity and exothermic behaviour to varying degrees.

Peat of Brunei Darussalam shows a great potential for the removal of methylene blue (MB) and malachite green (MG) dyes from aqueous solution. Carefully controlled batch experiments performed by changing one parameter at a time indicate that the optimum time periods of agitation and settling required for maximum removal of MB are 2.0 and 1.0 h, respectively, while these values for MG are 4.0 and 1.0 h, respectively. The optimum pH is determined to be the ambient value, and under the optimum conditions, 90 % removal of both dyes was determined under laboratory conditions. The equilibrium adsorption data analyzed for various isotherm models suggest that the Sips and Redlich–Peterson (R–P) models are valid for MB and MG, respectively. Further, thermodynamic studies show that the adsorption of both dyes on peat is spontaneous and endothermic. The adsorption capacities (q max) of MB and MG dyes on peat are 0.45 and 0.31 mmol g−1, respectively. Characterization of the surfaces of peat before and after treatment of dyes by SEM and FTIR provides conclusive evidence of adsorption of both dyes. Kinetics studies indicate that the adsorption of both MB and MG dyes is favored toward the pseudo-second-order model, with a little contribution of MG to the pseudo-first-order model. These results suggest that peat is a potential low-cost adsorbent for the removal of MB and MG dyes.

Artocarpus odoratissimus (Tarap) skin shows great potential as an effective low-cost biosorbent for toxic dyes, methylene blue (MB), and methyl violet 2B (MV). The Langmuir adsorption isotherm leads to the maximum biosorption capacities of this biomass, whose point of zero charge was at pH 4.4, of 0.577 mmol g−1 (184.6 mg g−1) and 0.349 mmol g−1 (137.3 mg g−1) for MB and MV, respectively. The Sips isotherm model is the best fit for adsorption of MB, while both the Langmuir and Sips models are in good agreement for MV. Mass transfer of dye species from solution to the biosorbent phase is fast with 50% dye being removed in less than 1 min following the pseudo-second-order kinetics.

Investigation of the electrical properties of polymer–clay nanocomposites is important in the development of nanoelectronic devices. These nanocomposites may be prepared by intercalating suitable monomers within interlayer spaces of expanding layered clay materials, followed by in situ polymerization. We made use of this approach to prepare montmorillonite–polyaniline nanocomposites by ion-exchanging the intergallery cations for anilinium ions and subsequently polymerizing the anilinium ions by peroxydisulphate in the acidic medium to yield emeraldine salt form of polyaniline intercalated in montmorillonite (ES1-MMT). The emeraldine salt form of polyaniline contains one positive charge per three monomer units, and hence, polymerization of anilinium ions reduces the number of cations present within the interlayer. Charge compensation thus requires uptake of required amount of cations from the solution. Further, the emeraldine salt form of polyaniline can be neutralized by treating with excess base such as ammonia. Thus, the neutralization of emeraldine salt results in an uptake of ammonium ions for charge balance. We have, therefore, neutralized ES1-MMT using aqueous ammonium hydroxide, and the cations inserted into the interlayer were again exchanged for anilinium ions. The latter was polymerized in acidic medium to yield more polyaniline in its emeraldine salt form (ES2-MMT). By repeating this procedure we have also prepared ES3-MMT. X-ray diffraction (XRD) spectra recorded at 150 °C reveal the enhancement of d-spacing upon increased amounts of polymer formation, and the Fourier transform infrared (FTIR) analysis also supports this by showing enhanced absorption due to bands typical of emeraldine salt (for example, B–NH+ = Q, where B and Q stand for benzanoid and quinoid, respectively). Careful analyses of FTIR spectra reveal that the polymer is present within the interlayers, as well as adsorbed onto the external surfaces and is bound to clay layers through hydrogen bonding. In this publication, we report the electrical properties of such ES-MMT nanocomposites. Alternating current (AC) impedance analysis shows that the nanocomposites are highly conducting materials, and their bulk conductivity enhances in the order ES1-MMT < ES2-MMT < ES3-MMT. The materials are pure electronic conductors as revealed by the direct current polarization studies. Further, their conductivities decrease with increasing temperature as of pure electronic conductors. By treating kaolinite with anilinium ions in acidic medium followed by peroxydisulphate ions, emeraldine salt–kaolinite (ES-KAL) composites have also been prepared. Because kaolinite is a non-expanding clay, the ion exchange is not possible, and hence, the polymer cannot be incorporated into the interlayer. This is indeed shown in the XRD analysis. The polymer can only reside out of the kaolinite particles. FTIR spectra reveal the hydrogen bonding between the polymer and kaolinite outer surfaces. AC impedance spectra of ES-KAL do not show high bulk conductivity. Thus, the comparison of AC impedance spectra of ES-KAL with ES-MMT systems clearly indicates that the bulk conductivity of the latter systems is predominantly due to intercalated polyaniline.

A series of polyaniline-Fuller's Earth (PANI-FE) nanocomposites were prepared by the successive intercalation of anilinium ions followed by polymerisation within the interlayer spaces of Fuller's Earth (a type of calcium montmorillonite). The first member in the series is prepared by exchanging the calcium ions in Fuller's Earth for ammonium ions and subsequently for anilinium ions and polymerising the latter using an externally introduced oxidant. The emeraldine salt form of polyaniline formed is then neutralised with ammonium hydroxide and more anilinium ions are exchanged for ammonium ions and polymerised to get the second member. In this manner, by making use the unique chemistry of clay and polyniline, four members of PANI-FE are prepared. In the last member, the negative layer charges of Fuller's Earth is completely neutralised by the positive charges of the polymer. The extent of polymer loading in each stage, the effect polymer has on the host structure and the electronic and ionic components of the conductivities of the new PANI-FE nanocomposites are investigated. The Fe(III) sites in FE are capable of spontaneously polymerising aniline within its intergalleries. The extent of spontaneous polymerisation is limited by the amount of Fe(III) present in the FE. The deliberate polymerisation of remaining anilinium ions by externally introduced oxidant results in highly conductive emeraldine salt-FE (EMS-FE) nanocomposites. The FE host accommodates higher amount of emeraldine salt and the repetitive insertions of the polymer could be done four times for complete layer charge neutralisation whereas with Bentonite the layer charge saturation takes place with three successive insertions. The new EMS-FE nanocomposites exhibit more than order of magnitude greater tuneable ionic and electronic conductivities compared to those of the same polymer incorporated in Bentonite.

Cu(II)-exchanged montmorillonite [Cu(II)-MMT] takes up pyrrolium ions by ion exchange. Two pyrrolium ions are inserted for each Cu(II) ion expelled from its interlayers. These pyrrolium ions undergo spontaneous polymerization because of the remaining Cu(II) ions present within the intergalleries to form Cu(I)-polypyrrole-MMT nanocomposite. The polypyrrole (PPY) dispels any water already present within the intergalleries and the material becomes hydrophobic and reluctant to take up water. The inherent d-spacing due to anhydrous PPY present within the intergalleries is 16.0 A, which is a 6.4 A enhancement from the situation, which contains a bare inorganic ion. The material possesses unusually high mixed electrical conductivity. The conjugation length (and hence the electronic conductivity) decreases as the temperature is increased as confirmed by the Fourier transform infrared spectroscopy. However, the ionic component of the conductivity increases with temperature. The temperature dependence of conductivity shows Arrhenius behavior but two different activation regions are clearly visible. The activation energy for Cu(I) migration within the nanocomposite is much lower than 100 C (Ea1/4 0.09 eV). At the higher temperature region, the activation energy is 0.23 eV and this value is also comparatively low suggesting the favorable motion of Cu(I) ions within the PPY-MMT nanocomposite thus making it a fast Cu(I) ion conductor. The ionic conductivities are in the range 0.66-1.15 mS cm 1 in the temperature range from 25 to 120 C.

This paper describes the preparation and characterization of conducting polyaniline-montmorillonite (PANI-MMT) nanocomposites by the polymerization of anilinium ions within the interlayer space of MMT particles. A procedure for the successive introduction of PANI chains within the interlayer galleries of MMT is developed. The d-spacing, measured after heat treatment at various temperatures serves as a measure of the amount of polymer inserted in the clay intergalleries. The FTIR spectroscopy reveals the presence of host-guest interactions of a hydrogen-bonded nature. The DC conductivities were found to increase with the amount of PANI intercalated. Anilinium ions supported on kaolinite tended to dislodge from the surface upon repeated washings, as shown by the absence of polymer formation on such samples upon treatment with the oxidant. In MMT, however, polymerization is observed even with exhaustively washed samples, thus confirming that the successive polymerization processes occur within the interlayer galleries. Exclusion of the washing stage gives a composite material in which polyaniline is present on both the internal and external surfaces. This material is found to have significantly higher electronic conductivities than the composites where the polymer is restricted to interlayer galleries. The washed samples of the polymer once loaded into the clay (EMS1-MMT), twice loaded into the clay (EMS2-MMT) and thrice loaded into the clay (EMS3-MMT) have electrical conductivities of 4.5 × 10−5, 3.0 × 10−4, and 1.0 × 10−3 Scm−1, respectively in their dry states. The corresponding samples prepared by excluding the washing procedure had the values of 4.0 × 10−4, 1.0 × 10−2, and 1.0 10−1 Scm−1, respectively.

This work reports the potential use of peel of breadnut, Artocarpus camansi , as an effective low-cost biosorbent for the removal of methylene blue (MB). Oven dried A. camansi peel (ACP), which had a point of zero charge at pH = 4.8, showed maximum biosorption capacity which was far superior to most literature reported fruit biomasses, including samples that have been activated. Isotherm studies on biosorption of MB onto ACP gave a maximum biosorption capacity of 409 mg g −1 . The Langmuir model was found to give the best fit among various isotherm models investigated and error analyses performed. Kinetics studies were fast with 50% dye being removed in less than 8 min from a 50 mg L −1 dye solution and further, kinetics followed the pseudo second order. Thermodynamic studies indicated that the biosorption process was both spontaneous and exothermic. Fourier transform infrared (FT-IR) of ACP before and after MB adsorption was investigated. It can be concluded that oven dried breadnut peel is a highly promising low-cost biosorbent with great potential for the removal of MB.

This research is on the evaluation of biosorption capability of the core of Artocarpus odoratissimus (Tarap), grown in Brunei Darussalam, towards Cd(II) and Cu(II) ions present in synthetic solutions, and to characterize the surface of Tarap particles. Thermogravimetric analysis and surface titrations were conducted to characterize the surface of dried Tarap core particles. Atomic absorption spectroscopic measurements were conducted to determine the extent of removal of Cd(II) and Cu(II) under different experimental conditions. Mass reductions associated with many exothermic reaction peaks were observed beyond 200°C up to 650°C indicating the combustion of organic matter in Tarap. Dried particles of core of Tarap bear a negative surface charge promoting strong interaction towards positively charged ions, such as Cu(II) and Cd(II). Biosorption of the two metal ions on Tarap, which is relatively high beyond pH = 4, occurs within a short period of exposure time. The extent of biosorption is enhanced by acid treatment of the biosorbent, and further it does not significantly depend on the presence of nonreacting ions up to an ionic strength of 2.0 M. Strong attraction between each metal ion and the biosorbent is attributed to the negative surface charge on the biosorbent within a broad pH range. Acid treatment of the biosorbent improves sorption characteristics, suggesting that ion exchange plays an important role in the metal ion—biosorbent interaction process.

The importance of a number of techniques (including1H and13C NMR, XRD and IR) in exploring the important catalytic properties of synthetic and natural clays is described. A clear distinction is observed between proven catalytically-active clays (e.g. Al-exchanged) and those which are generally less effective (e.g. Na-exchanged).13C NMR spectroscopy is used to identify directly products formed within the interlayer regions, and temperature-controlled powder XRD serves as a useful tool for identifying whether or not intercalation occurs under variously defined conditions. High-pressure XRD is used to verify the formation of different products during reaction.

High-resolution solid-state NMR ( 29 Si and 27 Al), as well as Fourier transform IR and X-ray diffraction are shown to be of considerable value in characterizing pillared clays and various un-pillared clays consisting of one or other of the following interlamellar ions: Li + , Na + , Cs + , NH + 4 and Al 3+ . The catalytic activities of clays prior to and after pillaring are briefly discussed.

29 Si MAS NMR spectra of zeolites are much simplified following dealumination and the resulting spectra yield a quantitative correlation between chemical shift and tetrahedral angle. This correlation is useful in the structural elucidation of zeolites, silicas and other aluminosilicates.

Evidence is provided for two alternative pathways for the reactions undergone by 2-methylpropene between the layers of a sheet silicate catalyst (Al3+-exchanged montmorillonite). This clay, when it initially contains ca. 12% interlayer water, catalyses the addition of either water or methanol to 2-methylpropene to yield, respectively, t-butanol or 2-methoxy-2-methyl propane (methyl tertiary butyl ether, MTBE), whereas the same clay following deliberate dehydration acts as an effective catalyst for the oligomerisation of 2-methylpropene, Similar results are obtained with an Al3+-exchanged synthetic hectorite.

Direct 57Fe-Mossbauer-spectroscopic evidence is presented for the involvement of lattice-subsituted iron(III) as an electron-accepting site, within montmorillonite, following intercalation of the clay by benzidine which results in the production of benzidine radical cations. The subsequent oxidation of the resulting iron(II), by dehydration of the benzidine blue–montmorillonite intercalate, is explained in terms of two simple equilibria which are set up at the clay surfaces. New Lewis-acid sites [involving iron (III)], created by oxidation of the original (ironII) ions in the clay, have been found to be active even under conditions where it is expected that benzidine species are present only at external surfaces of the montmorillonite.

Aniline is produced in good (ca. 45%) yield when the intercalate of montmorillonite and 4,4′-diamino-trans-stilbene is heated, in vacuo, to ca. 300 °C.

TRANSITION metal, ion-exchanged montmorillonites form complexes1,2, often of an interlamellar kind (intercalates), with a range of aromatic molecules, including benzene, toluene and the xylenes, anisole, and other species such as trans-stilbene and indene3–5. The aromatic molecules can form two main types of complex with the interlayer transition-metal ions, for example Cu(II). In the first type there is thought to be an edge-π-bonded copper arene moiety, similar to the bonding situation which exists in C6H6CuAlCl4 (ref. 6), and in the second instance it is considered to be a type of bond which causes associated distortion of the aromatic ring and some localisation of the circumferential double bonds1. Although detailed crystallographic analyses of the organic intercalates of sheet silicates has only recently commenced (ref. 7, and J. M. Adams et al., unpublished) and in spite of the paucity of information relating to the precise nature of the bonding of organic entities to encaged metal ions, it is clear2–4 that these organic complexes display a rich range of unusual reactions, some new examples of which we report here.

TRANSITION metal, ion-exchanged montmorillonites form complexes1,2, often of an interlamellar kind (intercalates), with a range of aromatic molecules, including benzene, toluene and the xylenes, anisole, and other species such as trans-stilbene and indene3–5. The aromatic molecules can form two main types of complex with the interlayer transition-metal ions, for example Cu(II). In the first type there is thought to be an edge-π-bonded copper arene moiety, similar to the bonding situation which exists in C6H6CuAlCl4 (ref. 6), and in the second instance it is considered to be a type of bond which causes associated distortion of the aromatic ring and some localisation of the circumferential double bonds1. Although detailed crystallographic analyses of the organic intercalates of sheet silicates has only recently commenced (ref. 7, and J. M. Adams et al., unpublished) and in spite of the paucity of information relating to the precise nature of the bonding of organic entities to encaged metal ions, it is clear2–4 that these organic complexes display a rich range of unusual reactions, some new examples of which we report here.

Aniline is produced in good (ca. 45%) yield when the intercalate of montmorillonite and 4,4′-diamino-trans-stilbene is heated, in vacuo, to ca. 300 °C.

Clay minerals of the montmorillonite family provide a matrix on which radical cations of a variety of amines may be formed. The origin of the different colours associated with the benzidine (bzn)–. NNN′N′-tetramethylbenzidine (tbzn)–, and trans-4.4′-diaminostilbene (dsn)-montmorillonite complexes has been further elucidated by u.v. and visible reflectance and i.r. spectroscopy. It is established that both uni- and di-positive bzn radical cations and protonated bzn moieties can exist at the internal and external clay surfaces. This is in contrast to the situation which prevails for tbzn where only the unipositive radical cation and protonated moieties appear to be formed. The interaction of montmorillonite with dsn dihydrochloride is similar to that of bzn but the nature of the product is modified by the precence of protons in cation-exchange sites.

Various types of novel reactions (relevant in bio-organic, inorganic, and prebiological contexts) which can be effected within spaces between the layers, or at the surfaces, of sheet-silicate minerals are summarized. The colour reactions displayed by nine selected nitrogen-containing small aromatic molecules when they complex with montmorillonite are also briefly reviewed, together with the results of a quantitative adsorptive study of benzidine on this particular mineral. Concurrent measurement of Na+-ion release from, and uptake of benzidine by, the mineral, and X-ray measurements of interlayer spacings, clearly reveal pre- and post-intercalation stages of the formation of the complex.

The emergence points of dislocations at cleavage faces of natural barytes crystals have been identified using the etchpit technique. The alignments of these etchpits and the observation of slip traces both in as-grown and deliberately deformed crystals yield the active slip planes in this material. The results compare favourably with a recent independent study of natural barytes crystals employing the X-ray topographical technique. Comparisons are made between barytes and the isomorphous ammonium perchlorate. It is found that, with one notable exception, the dislocation structures of these two materials are identical and probably characteristic of the space group, Pnma. The slip systems are {201}[101]; {401}[010]; {110}〈text-decoration:overline110〉; {001}[010]; {010}[001]; {101}〈text-decoration:overline101〉 or {101}[010], {110}[001] and {201}[001], the last-named being active in barytes only. The important criterion when considering the γ-irradiation behaviour of these two materials is the thermal stability of the respective lattices.