O presente trabalho trata da preparação e da caracterização textural e espectroscópica de hidróxidos mistos lamelares de composição [Mg3-xCuxAl(OH)8](CO3)0,5.yH2O (x= 0,3; 0,6; 0,9; 1,2; 1,5; 1,8; 2,1; 2,4; 2,7 e 3,0), bem como do estudo da reatividade desses materiais na hidroxilação do fenol, utilizando peróxido de hidrogênio como oxidante. Os sólidos foram preparados através do método da co-precipitação e caracterizados por difratometria de raios X, análises elementares (C, H, N e metais) e termogravimétricas, medidas de área superficial e, também, pelas seguintes técnicas espectroscópicas: vibracional no infravermelho e espalhamento Raman, eletrônica de absorção no visível-infravermelho próximo e ressonância paramagnética eletrônica. Observou-se que quanto maior o conteúdo de cobre(II) nas amostras, maior é a tendência à formação de CuO. Materiais de coloração azul contendo apenas uma fase cristalina foram obtidos por co-precipitação no intervalo de pH 8-10 e efetuando as etapas de envelhecimento e secagem na temperatura ambiente. Quanto maior a quantidade de íons Cu2+ no hidróxido misto lamelar, menor a cristalinidade e a estabilidade térmica do material. Os espectros de EPR são anisotrópicos (parâmetros g// e g? bem definidos), indicando que os íons cobre(II) se encontram em sítio com simetria axial. À medida que a quantidade de Cu2+ nas amostras aumenta, ocorre uma diminuição no sinal do metal de transição, que pode ser interpretada como decorrência de um acoplamento antiferromagnético entre os íons cobre. Dados de espectroscopia vibracional sugerem que nos hidróxidos mistos há dois tipos de íons carbonato. Além disso, foi observado o fenômeno de abaixamento de simetria dos ânions CO32- ao longo do processo de aquecimento, originando, conforme a temperatura e a composição, materiais de coloração variada. O abaixamento de simetria pode estar sendo ocasionado pela coordenação (ou enxertia) dos íons carbonato aos centros metálicos das lamelas. Os sólidos verdes obtidos por aquecimento possuem, além de bandas no espectro eletrônico atribuídas às transições do tipo d-d (700-800 nm), absorção na região abaixo de 400 nm, que pode ser atribuída à transferência de carga O2- -> Cu2+. Apesar dos difratogramas de raios X apresentarem picos de baixas intensidades referentes às fases espinélio, a coloração ocre observada pode ser devida à presença da fase CuAl2O4 (sólido marrom). Nas amostras cinzas e pretas, os difratogramas de raios X mostram picos intensos atribuídos ao CuO. Os testes de reatividade dos hidróxidos mistos sintetizados na hidroxilação do fenol pelo peróxido de hidrogênio em meio aquoso envolveram a variação de parâmetros reacionais como temperatura, tempo, concentração de substrato e influência de luz, mantendo-se constante a relação molar fenol/Cu2+. O substrato orgânico foi oxidado a catecol, hidroquinona e p-benzoquinona. As substâncias no meio reacional foram quantificadas pela deconvolução do espectro eletrônico da mistura na região do ultravioleta. Como esperado, o material sintetizado sem íons cobre(II) não apresenta atividade catalítica para o sistema reacional estudado. / In this work it was investigated the preparation and spectroscopic characterization of layered hydroxides of composition [Mg3-xCuxAl(OH)8](CO3)0.5.yH2O (x = 0.3; 0.6; 0.9; 1.2; 1.5; 1.8; 2.1; 2.4; 2.7 and 3.0), as well the reactivity of these materials towards phenol hydroxylation, using hydrogen peroxide as oxidizing agent. The solids had been prepared through the co-precipitation method and characterized by X ray diffractometry, elemental analysis (C, H, N and metals), thermogravimetric analysis, surface area measurements, and also by the following spectroscopic techniques: infrared vibrational absortion (FTIR), Raman scattering, vis-NIR electronic absorption and electron paramagnetic resonance (EPR). It was observed that the increase of copper(II) content in the samples favours the CuO formation. Materials of blue coloration containing only one crystalline phase were obtained by the co-precipitation method in the pH range 10 – 8, and were submitted to aging and drying processes at room temperature. As the amount of Cu2+ ions increases in the layered hydroxide material, it was observed a decrease in crystallinity and thermal stability. EPR spectra are anisotropic (parameters g// and g? well defined), indicating that copper(II) ions are in sites with axial symmetry. As the amount of Cu2+ in the samples increases, EPR signal decreases, what can be interpreted as result of an antiferromagnetic coupling between copper ions. FTIR data suggests that the layered hydroxides gave two types of cabornate ions. Moreover, the symmetry lowering phenomena of CO32- anions during the heating process was observed, originating, according to the temperature and sample composition, materials of varied coloration. This lowering of symmetry can be due to coordination (or grafting) of carbonate ions to the metal ions in the layers. Vis-NIR electronic spectra of green solids obtained by heating show absorption in the region below 400 nm, besides bands attributed to d-d transitions (700-800 nm), that can be attributed to O2- -> Cu2+ charge transfer transition. Despite the X ray diffraction peaks of low intensities attributed to spinel phases, the ochre coloration observed can be due to the presence of CuAl2O4 (brown solid). For gray and black samples, X ray diffractograms shows intense peaks attributed to CuO. Reactivity tests about phenol hydroxylation involved the variation of experimental parameters as temperature, time, substrate concentration and influence of light, keeping constant the phenol/Cu2+ molar ratio. The organic substrate was oxidized to cathecol, hydroquinone and p-benzoquinone and these products were quantified by deconvolution of the electronic spectra. As expected, the material synthesized without copper(II) ions does not show catalytic activity for the studied reaction.

Thesis (Ph. D.)--Murdoch University, 1995. / Thesis submitted to the School of Mathematical and Physical Sciences. Includes bibliographical references (leaves 274-288).

Thesis (M.S.)--University of North Texas, May, 2008. / Title from title page display. Includes bibliographical references.

Thesis (Ph. D.)--University of North Texas, Aug., 2009. / Title from title page display. Includes bibliographical references.

Thesis (Ph. D.)--University of Washington, 1995. / Vita. Includes bibliographical references (leaves [186]-201).

Thesis (PhD.(Chemical Engineering)--University of Pretoria, 2005. / Includes bibliographical references.

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Submitted in fulfilment of the academic requirements for the Degree of Master's in Chemistry, Durban University of Technology, 2017. / Hydrotalcites (HT) and hydrotalcites-like (HTLc) compounds were synthesized by the co-precipitation method under low supersaturation. The synthesized binary Mg-Al hydrotalcites and ternary Cu/Mg-Al hydrotalcite-like compounds were characterized by various physico-chemical techniques such as inductively coupled plasma-optical emission spectroscopy (ICP-OES), powder X-ray diffraction (XRD), Fourier transform- infrared spectroscopy (FT-IR), ultraviolet-visible (UV-VIS) spectroscopy, thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and BET surface area analysis. Elemental composition generated from ICP-OES data revealed a value of x in the region of 0.25 to 0.33 for all the compounds except for the MgAl-11 sample which revealed an x value of 0.5 while XRD patterns exhibited characteristic features indicative of an ordered layered material. FT-IR spectra confirmed the presence of characteristic functional groups and interlayer anions. Only Cu2+ which has a d9 configuration was accountable for the bands identified in UV-VIS spectra, whereas both Mg and Al with their d0 electron configurations showed no absorptive bands in the UV-VIS spectra. During thermal treatment by TGA, typical weight loss of Cu-Mg/Al HTLcs with temperature elevation was observed. The SEM images clearly demonstrated that all the Cu-Mg/Al HTLcs retained their characteristically layered structure morphologies. The BET surface area measurements showed no trend, however the surface area decreased with an increase in the copper concentration in some cases. For the heterogeneous hydroxylation of phenol using H2O2 as an oxidant, several reaction parameters such as solvent systems, catalyst amount, temperature, substrate/oxidant ratio, time and solvent volume were investigated. The product stream, monitored by gas chromatography showed that catechol (CAT) and hydroquinone (HQ) were the main products. Non-catalytic (blank) experiments were investigated to determine whether the reactants and the internal standard contributes to the conversion of phenol without the use of a catalyst. All blank reactions showed very low phenol conversions which were less than 1%, whereas the Mg/Al HTs showed low phenol conversions as well. All the Cu-Mg/Al catalysts showed measurable phenol conversion with Cu-Mg/Al-51a giving the highest conversion of 29.9% and a 56 and 44% selectivity towards CAT and HQ, respectively. The Cu-Mg/Al-15b catalyst, which had the lowest copper concentration, showed the lowest phenol conversion of 8.3% with a 55 % CAT selectivity and 45% HQ selectivity. In general, the phenol conversion increased with an increase in copper concentration. This reinforced the hypothesis that copper was the active centre in this reaction, since no measurable conversion was observed with Mg/Al HTs. / M

The preparation of layered double hydroxides via co-precipitation of a divalent/trivalent metal solution against a base results in 1 mm LDH particles with a disorganized metal lattice. Research was performed to address these morphological issues using techniques such as Ostwald ripening and precipitation via aluminate. Another interesting issue in layered double hydroxide materials is the uptake and orientation of anions into the interlayer. Questions about iron cyanide interlayer anions have been posed. Fourier transform infared spectroscopy and powder x-ray diffraction have been used to investigate these topics. It was found that factors such as orientation, anion charge, and anion structure depended on the divalent/trivalent metal ratio of the hydroxide layer and reactivity time. The cyanide self-addition reaction is an important reaction of classical prebiotic chemistry. This reaction has been shown to give rise to amino acids, purines and pyrimidines. At cyanide concentrations similar to that expected on the early earth, hydrolysis to formamide rather than self-addition occurs. One theory to alleviate this side reaction is the use of minerals or clays that are thought to concentrate and catalyze prebiotics of interest. Layered double hydroxides have been studied as a catalyst for this reaction.