Copper- and zinc-bearing composite membranes for periodontal repair

Periodontitis (inflammation and destruction of the tooth attachment apparatus) is one of the most widespread diseases in the world. Polymer-bioactive glass composite membranes can be used for the guided tissue regeneration (GTR) of diseased periodontal structures. GTR involves the placement of the membrane to exclude soft epithelial and gingival tissues from the exposed tooth in order to facilitate the regeneration of the more slow-growing periodontal ligament and hard tissues. Bioactive glasses incorporating antimicrobial ions such as silver, zinc and copper have been shown to resist biomaterial-centred infection; although, the presence of these metal ions is reported to reduce bioactivity in some instances. Chitosan, a biodegradable carbohydrate polymer, is a popular choice for GTR membranes as its structure resembles that of bone extracellular matrix. In the present study, copper- and/or zinc-bearing bioactive glasses were prepared by the sol-gel process and incorporated into chitosan membranes by solvent-casting. The in vitro bioactivity and degradation rates of the chitosan-bioactive glass membranes were evaluated with respect to their potential use as GTR membranes

Interactions of Cd2+, Co2+ and MoO42- ions with crushed concrete fines

Construction and demolition activities generate approximately two thirds of the world’s waste with concrete-based demolition material accounting for the largest proportion. Primary aggregates are recovered and reused, although the cement-rich fine fraction is underutilised. In this study, single metal batch sorption experiments confirmed that crushed concrete fines (CCF) are an effective sorbent for the maximum exclusion of 45.2 mg g-1 Cd2+, 38.4 mg g-1 Co2+ and 56.0 mg g-1 MoO42- ions from aqueous media. The principal mechanisms of sorption were determined, by scanning electron microscopy of the metal-laden CCF, to be co-precipitation with Ca2+ ions released from the cement to form solubility limiting phases. The removal of Co2+ and MoO42- ions followed a zero-order reaction and that of Cd2+ was best described by a pseudo-second-order model. The Langmuir model provided the most appropriate description of the steady state immobilisation of Cd2+ and Co2+, whereas the removal of MoO42- conformed to the Freundlich isotherm. Long equilibration times (>120 h), loose floc formation and high pH are likely to limit the use of CCF in many conventional wastewater treatment applications; although, these properties could be usefully exploited in reactive barriers for the management of contaminated soils, sediments and groundwater

Mixed-phase ion-exchangers from waste amber container glass

This study investigated the one-pot hydrothermal synthesis of mixed-phase ion-exchangers from waste amber container glass and three different aluminium sources (Si/Al = 2) in 4.5 M NaOH(aq) at 100 °C. Reaction products were characterised by X-ray diffraction analysis, Fourier transform infrared spectroscopy, 27Al and 29Si magic angle spinning nuclear magnetic resonance spectroscopy and scanning electron microscopy at 24, 48 and 150 h. Nitrated forms of cancrinite and sodalite were the predominant products obtained with reagent grade aluminium nitrate (Al(NO3)3∙9H2O). Waste aluminium foil gave rise to sodalite, tobermorite and zeolite Na-P1 as major phases; and the principal products arising from amorphous aluminium hydroxide waste were sodalite, tobermorite and zeolite A. Minor proportions of the hydrogarnet, katoite, and calcite were also present in each sample. In each case, crystallisation was incomplete and products of 52, 65 and 49% crystallinity were obtained at 150 h for the samples prepared with aluminium nitrate (AN-150), aluminium foil (AF-150) and amorphous aluminium hydroxide waste (AH-150), respectively. Batch Pb2+-uptake (~100 mg g−1) was similar for all 150-hour samples irrespective of the nature of the aluminium reagent and composition of the product. Batch Cd2+-uptakes of AF-150 (54 mg g−1) and AH-150 (48 mg g−1) were greater than that of AN-150 (36 mg g−1) indicating that the sodalite- and tobermorite-rich products exhibited a superior affinity for Cd2+ ions. The observed Pb2+- and Cd2+-uptake capacities of the mixed-product ion-exchangers compared favourably with those of other inorganic waste-derived sorbents reported in the literature

Basic metallosilicate catalysts from waste green container glass

Environmental imperatives to conserve natural resources and to divert waste streams have stimulated significant interest in mineral recycling. This study illustrates that waste green container glass cullet is a suitable feedstock material for the facile synthesis of basic metallosilicate minerals that have potential as heterogeneous catalysts for industrially significant organic reactions. The target product phases, tobermorite (Ca⁠5Si⁠6O⁠16(OH)⁠2·4H⁠2O), lithium metasilicate (Li⁠2SiO⁠3) and hydroxycancrinite (Na⁠6Ca(AlSiO⁠4)⁠6(OH)⁠2·2H⁠2O) were synthesised by hydrothermal treatment of waste green cullet in alkaline media at 125°C for 14 days. The reaction products were characterised by powder X-ray diffraction analysis, Fourier transform infra-red spectroscopy and scanning electron microscopy. Phase-pure tobermorite (TB) was prepared from a mixture of glass and lime in sodium hydroxide solution. Impure lithium metasilicate (LS) containing minor proportions of portlandite and calcite was synthesised from the glass in lithium hydroxide solution. A mixed product of hydroxycancrinite (HC), with minor proportions of hydroxysodalite, tobermorite and hydrogarnet, was produced from the glass in a solution of aluminium and sodium hydroxides. All three glass-derived metallosilicate products were found to be effective catalysts for the Knoevenagel synthesis of ethyl (2E)-2-cyano-3-phenylacrylate from ethyl cyanoacetate and benzaldehyde. The order of catalytic efficacy followed the trend in basicity of the metallosilicate products, LS >TB > HC

Synthesis of feldspathoids and zeolite K-F from waste amber container glass

The hydrothermal formation of mineral products from a mixture of amber container glass and aluminium waste (Al:Si = 1) in 4 M NaOH(aq) or 4 M KOH(aq) at 100 °C was monitored at 1, 3 and 10 days by X-ray diffraction analysis with Rietveld refinement, Fourier transform infrared spectroscopy and scanning electron microscopy with energy dispersive X-ray analysis. In NaOH(aq), at 1, 3 and 10 days, respectively, 48%, 55% and 63% of the glass crystallised to form hydroxysodalite (HS) and hydroxycancrinite (HC) with minor proportions of katoite and tobermorite. The partial successive transformation of HS to HC was also observed with time. The initial rates of dissolution of the glass and formation of the principal zeolite K-F and secondary katoite phases were considerably slower in KOH(aq); although, the subsequent development of the products was greater than that in NaOH(aq). The zeolite K-F product achieved only 5% crystallinity within the first day which then increased markedly to 60% and 78% at 3 and 10 days, respectively. Despite the incomplete conversion of amber glass into crystalline zeolitic phases, the uptake capacities of the 10-day feldspathoid and zeolite K-F products for Pb2+ (4.3 and 4.5 meq g-1, respectively) and Zn2+ (3.9 and 4.1 meq g-1, respectively) ions compared favourably with those of many other zeolites and waste-derived inorganic sorbents reported in the literature

Hydrothermal synthesis of zeolites from green container glass

Landfilling and stockpiling unrecycled colored container glass represents a considerable failure in sustainability with respect to the conservation of energy and mineral resources. In this study, the single-step hydrothermal synthesis of low-silica zeolites from a mixture of waste green container glass and aluminum foil (Al:Si = 1) in 4 M NaOH(aq) at 125 °C was followed at 1, 3, 7 and 14 days. The principal phases, sodalite and cancrinite, appeared within 1 day accompanied by minor quantities of hydrogarnet and tobermorite arising from a stoichiometric excess of calcium ions in the parent glass. Products of 63, 67, 71 and 72% crystallinity were obtained at 1, 3, 7 and 14 days, respectively, with partial successive conversion of sodalite to cancrinite over time. Ion-exchange and catalytic applications of sodalite and cancrinite arise from the high anionic charge of the 1:1 ratio of alternating SiO44- and AlO45- units within their aluminosilicate frameworks. In this respect, the uptake capacity of the 14-day zeolitic product for Cu2+ and Cd2+ ions (1.58 meq g-1 and 1.66 meq g-1, respectively) was within the expected range for zeolites and compared favorably with those reported for other inorganic sorbents derived from industrial and municipal wastes. The 14-day product was also found to be an effective basic heterogeneous catalyst for the Knoevenagel condensation reaction