Synthesis of calcium peroxide nanoparticles as an innovative reagent for in situ chemical oxidation

doi:10.1016/j.jhazmat.2011.06.060

Journal of Hazardous Materials

Volume 192, Issue 3, 15 September 2011, Pages 1437-1440

https://doi.org/10.1016/j.jhazmat.2011.06.060 Get rights and content

Abstract

Chemical oxidation is one of the many different methods of site remediation that has emerged lately as an alternative method to traditional techniques. According to this research calcium peroxide is suitable choice for contaminant biodegradation in soil and ground water but speed of oxidation reaction between calcium peroxide and contaminant is slow. Synthesis of calcium peroxide in nano size by increased ratio of surface to volume can increase the speed of reaction and solve the problem. We have developed a simple surface modification technique to avoid irreversible agglomeration of calcium peroxide nanoparticles. The technique is based on hydrolysis–precipitation procedure, using CaCl₂ as a precursor. Polyethylene glycol 200 (PEG200) is used as a surface modifier. CaO₂ was identified and studied by characterization techniques, including XRD and TEM. The results indicate the ability of this method for synthesis of new reagent in nano size and improve quality of in situ chemical oxidation. Size determination by TEM image indicates the size of calcium peroxide nanoparticles approximately 15–25 nm.

Highlights

► We introduce CaO₂ nanoparticles as an efficient for in situ chemical oxidation reactions. ► Oxygen releasing rate of calcium peroxide in the nano size will increase comparison of CaO₂. ► Because of the stabilizer material used in this process is recyclable, this process has a high economic justification.

Introduction

In situ chemical oxidation (ISCO) is based on the delivery of chemical oxidants to contaminated media in order to either destroy the contaminants by converting them to innocuous compounds commonly found in nature. ISCO is being used for ground water, sediment, and soil remediation. It can be applied to a variety of soil types and sizes (silt and clay). Chemical oxidation has been shown to be effective at the destruction of the dissolved phase of non-aqueous phase liquids, which are known to be difficult to remediate through other tactics. Therefore, if administered correctly, ISCO has the potential to be a low-cost, fast, effective, and relatively low maintenance remediation technology [1].

The four main species used today in ISCO industry are permanganate, persulfate, hydrogen peroxide, and calcium peroxide. The characteristics of four main species used in ISCO are given in Table 1. Permanganate is frequently sold in the form of the salt potassium permanganate. It is a well-known and widely used oxidant in ISCO [2], [3], with a few benefits and limitations. The most well-known limitations of permanganate are that it has a long half-life. This long half-life is that permanganate is a less powerful oxidative species [4].

Persulfate is frequently sold in the form of the salt sodium persulfate, Na₂S₂O₈, and is in many ways similar to permanganate. Persulfate does suffer from the fact that it generates sulfate during cleanup, which has a secondary maximum contaminant levels (MCLs). This MCL is much higher than the MCL for manganese: 250 mg/L for sulfate, as opposed to 0.05 mg/L for manganese. Persulfate, like permanganate, also has been shown to have little impact on naturally occurring bacteria colonies, and therefore should not inhibit bioremediation to any significant degree [4].

Hydrogen peroxide is the oxygen source most commonly used to ISCO for bioremediation applications. Hydrogen peroxide decomposes to form molecular oxygen and water in the presence of catalase (an enzyme found in aerobic microorganisms. and certain abiotic catalysts) [5]. Virtually all aerobic microorganisms produce catalase [6]. Hydrogen peroxide can be effective in promoting contaminant biodegradation in soil [7], [8], but is readily scavenged by metals and humic substances. This results in rapid exhaustion of the oxygen source [9]. Oxygen released at a rate greater than by which it can be consumed by microorganisms escapes unused via volatilization or dissolved in groundwater. Furthermore, hydrogen peroxide can be toxic at concentrations required to achieve biological treatment [7], [9].

Recent studies suggest that calcium peroxide (CaO₂) is a more effective source of H₂O₂ for ISCO than liquid H₂O₂ [10], [11]. CaO₂ dissolves to form H₂O₂ and Ca(OH)₂, liberating a maximum of 0.47 g H₂O₂/g CaO₂ [12]. The advantage is that the released H₂O₂ is auto-regulated by the rate of CaO₂ dissolution, reducing disproportionation since not all the H₂O₂ is available at once as with liquid H₂O₂. Ndjou’ou and Cassidy compared the treatment of a soil contaminated with petroleum hydrocarbons using a commercially available CaO₂-based oxidant and liquid H₂O₂ at pH of 8. CaO₂ removed 96% of total petroleum hydrocarbons (TPH), compared with 74% using liquid H₂O₂ [11]. Several studies have reported that addition of calcium peroxide in saturated soil and ground water is suitable choice for contaminant degradation [13], [14], [15], [16], [17], [18], [19], [20], [21]. But the rate of the oxidation reaction between calcium peroxide and contaminant is slow. Synthesis of calcium peroxide in nano size can increase the ratio of surface to volume, so increase the speed of reaction and solve the problem [22].

The aim of our work is development of a simple surface modification technique to avoid irreversible agglomeration of calcium peroxide nanoparticles. The technique is based on hydrolysis–precipitation procedure, using CaCl₂ as a precursor. Polyethylene glycol 200 (PEG200) is used as a surface modifier. CaO₂ was identified and studied by a variety of characterization techniques, including XRD and TEM. The result indicates the ability of this method for synthesis of new Fenton reagent in nano size and improve quality of in situ chemical oxidation. Size determination by TEM image indicate the size of calcium peroxide nanoparticles is approximately 15–25 nm.

Section snippets

Materials

Calcium chloride (Merck, 99.5%); hydrogen peroxide aqueous solution H₂O₂ (Merck, 35%); PEG 200, H(OCH₂CH₂)nOH (Fluka), ammonia (Merck, 25%), silver nanoparticles (NANOPAC PERSIA Co.) and sodium hydroxide, NaOH (Merck) were used in their commercial forms.

Preparation of CaO₂ nanoparticle solution

Three grams of calcium chloride was dissolved in 30 mL distilled water, 15 mL ammonia solution (1 M) and one 120 mL of PEG 200 was added to the stirring mixture. Then 15 mL of 30% H₂O₂ was added to the mixture by rate of 3 drops per minute. The

Characterization of the CaO₂ nanoparticles

There are two general methods for synthesizing peroxides [23]. The first involves heating the oxide in a stream of pure, CO₂-free dry oxygen. This method is favored for making peroxides that are considerably more stable than the corresponding oxide, for example, for the preparation of BaO₂. In fact, BaO₂ is commercially made by heating BaO at 500 °C in flowing, pure oxygen. The synthesis of the less stable SrO₂ requires more drastic conditions, namely heating the oxide at a temperature of 350 °C

Conclusion

Stabilized nanoparticles of calcium peroxide were formed by an improved and simple technique. The process is spontaneous and no additional equipment or energy source is required. The calcium peroxide preparation method is based on oxidation–hydrolysis–precipitation procedure, with polyethylene glycol 200 as a surface modifier. Pure, stabilized nanoparticles of calcium peroxide remained in the nano-scale during all stages.

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Synthesis of calcium peroxide nanoparticles as an innovative reagent for in situ chemical oxidation

Abstract

Highlights

Introduction

Section snippets

Materials

Preparation of CaO2 nanoparticle solution

Characterization of the CaO2 nanoparticles

Conclusion

J. Contam. Hydrol.

J. Contam. Hydrol.

J. Contam. Hydrol.

Chemosphere

Chemosphere

Int. J. Environ. Waste Manage.

Anal. Chem.

In situ oxidation remediation technologies: kinetic of hydrogen peroxide decomposition on soil organic matter

J. Hazard. Mater.

Comparative study of the effect of four ISCO oxidants on PCE oxidation and aerobic microbial activity

Hydrogen Peroxide

Microbial Ecology: Fundamentals and Applications

Effect of oxygen amendments and soil pH on bioremediation of industrially contaminated soils

Energy Sources

Preparation of CaO₂ nanoparticle solution

Characterization of the CaO₂ nanoparticles