Abstract
We explore a more concise process for the preparation of high-purity alumina and to address the problem of some conventional micro- and nano-adsorbents having difficulty in exposing their adsorption sites to target pollutants in solution due to the heavy aggregation of the adsorbent, which confers poor adsorption properties. The methods of using gamma-phase high-purity mesoporous alumina (HPMA), with its excellent adsorption properties and high adsorption rates of Congo Red, and of using lower-cost industrial aluminum hydroxide by direct aging and ammonium salt substitution were successfully employed. The results showed that the purity of HPMA was as high as 99.9661% and the total removal rate of impurities was 98.87%, a consequence of achieving a large specific surface area of 312.43 m2 g−1, a pore volume of 0.55 cm3 g−1, and an average pore diameter of 3.8 nm. The adsorption process was carried out at 25 °C, the concentration of Congo Red (CR) dye was fixed at 250 mg L−1 and the amount of adsorbent used was 100 mg. The HPMA sample exhibited an extremely fast adsorption rate in the first 10 min, with adsorption amounts up to 476.34 mg g−1 and adsorption efficiencies of 96.27%. The adsorption equilibrium was reached in about 60 min, at which time the adsorbed amount was 492.19 mg g−1 and the dye removal rate was as high as 98.44%. One-hundred milligrams of adsorbent were weighed and dispersed in 200-mL CR solutions with mass concentrations ranging from 50–1750 mg L−1 to study the adsorption isotherms. This revealed that the saturation adsorption capacity of the produced HPMA was 1984.64 mg g−1. Furthermore, the process of adsorbing Congo Red in the synthesized product was consistent with a pseudo-second order model and the Langmiur model. It is expected that this method of producing HPMA will provide a productive, easy and efficient means of treating toxic dyes in industrial wastewater.
Highlights
High-purity alumina (HPA), one of the cutting-edge materials of the 21st century, is widely used in modern industrial products for its excellent physical and chemical properties, for instance, high strength wear and corrosion-resistant candle materials, special gas additives, advanced ceramic materials, catalysts and their carriers, biomedical, protective materials, single crystal materials, laser crystals and many other fields [1,2,3,4,5,6,7,8,9,10,11]
The overall impurity removal rate, on the other hand, increased from 97.97% to 98.86% and decreased to 98.15% and the purity of alumina rises from 99.9393% to 99.9661% and falls to 99.9447%
It can be seen from the X-ray diffraction (XRD) patterns (Figure 6) that the product is γ- Al2O3 with no significant change in the crystalline phase when roasted at 500–700 °C; this partly occurs in the product-phase transformation from γ-Al2O3 to the θ-Al2O3 crystalline phase when roasted at 900 °C, and to the θ-Al2O3 crystalline phase, which has a small specific surface area (JCPDF Card: No 11-0517) and is completely formed at 1100 °C. θ-Al2O3 is the most stable tripartite crystalline system among all alumina phases; it has a low specific surface area and weak chemical activity, so it is not suitable for the preparation of adsorbents or catalysts
Summary
High-purity alumina (HPA), one of the cutting-edge materials of the 21st century, is widely used in modern industrial products for its excellent physical and chemical properties, for instance, high strength wear and corrosion-resistant candle materials, special gas additives, advanced ceramic materials, catalysts and their carriers, biomedical, protective materials, single crystal materials, laser crystals and many other fields [1,2,3,4,5,6,7,8,9,10,11]. In the presence of a catalyst, metallic aluminum and organic alcohol are mixed and reacted to obtain an alcohol–aluminum solution, which is followed by hydrolysis and high-temperature roasting of the intermediates to synthesize HPA products The advantage of this method is the high purity and small particle size of the prepared alumina products, whereas, its high production cost and its being a complicated and uncontrollable process limit its economic efficiency. Congo Red (CR), a water-soluble acidic anionic azo pigment, is commonly used in the textile industry because of its strong adsorption to cellulose; the discharge of wastewater in the textile industry contains Congo Red components It can affect aquatic organisms and the food chain, even if the CR concentration in water is very low [21], such as by increasing chemical oxygen demand (COD) at the water surface and interfering with sunlight penetration through the water surface, reducing photosynthetic activity [22]. The other analytically pure reagents used, hydrochloric acid, ammonium oxalate, ammonium acetate and ammonium carbonate, were all purchased from Xi-long Chemical Co., Shantou, China, and were used without any pretreatment
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