Inez Hua

Sonochemical Degradation of p-Nitrophenol in a Parallel-Plate Near-Field Acoustical Processor

The sonochemical degradation of p-nitrophenol (p-NP) in a near-field acoustical processor (NAP) is investigated. The pseudo-first-order rate constant, k, for p N P degradation increases proportionally from 1.00 x to 7.94 x 10^(-4) s^(-l) with increasing power to volume ratio (i.e., power density) over the range of 0.98-7.27 W/cm^3. An increase in the power-to-area ratio (i.e., sound intensity) results in an increase in k up to a maximum value of 8.60 x 10^(-4) s^(-1) a sound intensity of 1.2 W/cm^2. A mathematical model for a continuous-flow loop reactor configuration is required in order to extract k from the experimentally observed rate constant, k_(obs), which is a function of the relative volumes of reactor and reservoir. The nature of the cavitating gas (Ar, O_2) is found to influence the overall degradation rate and the resulting product distribution. The rate constant for p-NP degradation in the presence of pure O_2, k_(O_2), = 5.19 x 10^(-14) s^(-1), is lower than in the presence of pure Ar, k_(Ar) = 7.94 x 10^(-4) s^(-1). A 4:l (v/v) Ar/O_2 mixture yields the highest degradation rate, k_(Ar/O_2) = 1.20 x 10^(-3) s^(-1). Results of these experiments demonstrate the potential application of large-scale, high-power ultrasound to the remediation of hazardous compounds present at low concentrations. The NAP is a parallel-plate reactor that allows for a lower sound intensity but a higher acoustical power per unit volume than conventional probe-type reactors.

Enhanced sonochemical decomposition of 1,4-dioxane by ferrous iron

The enhanced ultrasonic decomposition of 1,4-dioxane by the addition of ferrous iron (Fe(II)) was investigated at 205, 358, 618, and 1071 kHz. The total organic carbon (TOC) remaining was also determined at each frequency. Addition of Fe(II) improved the 1,4-dioxane decomposition rate and mineralization efficiency at all frequencies studied. A nearly four-fold increase of the rate constant was observed at the optimal Fe(II) concentration and a frequency of 205 kHz. In the presence and absence of the iron, the fastest overall degradation and mineralization of 1,4-dioxane took place at 358 kHz where 95% of the initial 1,4-dioxane was removed after 50 min. Finally, although reduced, the ultrasonic decomposition of 1,4-dioxane was still significant at all frequencies in the presence of the hydroxyl radical scavenger bicarbonate.

Ultrasonic Irradiation of Dichlorvos: Decomposition Mechanism

The sonochemical degradation of dichlorvos in a batch reactor is investigated. Dichlorvos was irradiated with 500 kHz ultrasound at input powers ranging from 86 to 161 W. Acoustic power and sparge gas are two factors which greatly affect sonochemical degradation efficiency. Increasing total acoustic power input from 86 to 161 W resulted in a change in the rate constant from 0.018 +/- 0.001 min-1 to 0.037 +/- 0.002 min-1. The change in rate constant due to sparge gas (Argon, Oxygen, and Argon/Oxygen (60/40% v/v) mixture) at a power of 161 W is also investigated, with the Argon/Oxygen mixture giving the highest rate constant (0.079 +/- 0.005 min-1). Total organic carbon and ion chromatographic analyses are employed to determine and quantify major degradation products, including dimethyl phosphate, formate, carbon dioxide, chloride, and phosphate. The extent of mineralization, indicated by a decrease in the total organic carbon, and the formation of the various intermediates and products, varies with saturating gas. A pathway for dichlorvos decomposition is proposed, based upon formation rates of the various intermediates and products and the rate of decrease of the total organic carbon in the system. The limiting steps in the mineralization pathway appear to be transformation of dimethyl phosphate and formate.

Ultrasonic irradiation of carbofuran: decomposition kinetics and reactor characterization

The sonochemical decomposition of carbofuran (2,3-dihydro-2,2-dimethyl-7-benzofuranyl,C12H15NO3) in a parallel plate near-field acoustical processor (NAP) is reported. Ultrasonic irradiation was performed at 16 and 20 kHz, under a total applied power of 1800 W. Carbofuran decomposition was enhanced with increasing power densities (1.65 W mL-1-5.55 W mL-1), and with decreasing initial concentrations (25 microM vs. 130 microM). The nature of the dissolved gas in solution also influenced the observed decomposition rate. The hydrodynamic behavior of the NAP reactor was characterized by calculating the Reynolds numbers and by performing tracer studies with a conservative tracer, sodium chloride (NaCl). The calculated dispersion coefficients indicate an intermediate amount of dispersion during operation of the reactor.

Hydrogen peroxide-assisted UV photodegradation of Lindane.

Aqueous solutions of gamma-hexachlorocyclohexane (Lindane) were photolyzed (lambda=254 nm) under a variety of solution conditions. The initial concentrations of hydrogen peroxide (H(2)O(2)) and Lindane varied from 0 to 20 mM and 0.21 to 0.22 microM, respectively, the pH ranged from 3 to 11, and several concentration ratios of Suwannee River humic acid and fulvic acid were dissolved in the irradiated solutions. Lindane rapidly reacted, and the maximum reaction rate constant (9.7 x 10(-3) s(-1)) was observed at pH 7 and initial [H(2)O(2)]=1 mM. Thus, 90% of the Lindane is destroyed in approximately 4 min under these conditions. In addition, within 15 min, all chlorine atoms were converted to chloride ion, indicating that chlorinated organic by-products do not accumulate. The reactor was characterized by measuring the photon flux (7.04 x 10(-6) E s(-1)) and the cumulative production of *OH during irradiation. The cumulative *OH production during irradiation was fastest at an initial [H(2)O(2)]=5 mM (k=0.77 micro M s(-1)).

Ultrasonic Degradation of Trichloroacetonitrile, Chloropicrin and Bromobenzene: Design Factors and Matrix Effects

Abstract Power ultrasound has been employed to degrade numerous environmental pollutants. Through a series of experiments, the viability of sonication for pollution control in higher complexity systems was investigated. First, a mixture of chloropicrin (CCl 3 NO 2 ), trichloroacetonitrile (C 2 Cl 3 N), and bromobenzene (C 6 H 5 Br) was irradiated in a batch system. At a frequency of 20 kHz and a sound intensity of 30.8 W cm −2 , a minimal difference was observed between rate constants during sonication of a mixture and rate constants during sonication of individual compounds. Ultrasonic irradiation at 358 kHz was also viable for treatment of a mixture characterized by a high chemical oxygen demand (COD=3470 ppm). Sonication in a complex aqueous matrix, river water, demonstrated minimal to moderate decreases in efficiency compared to sonication in reagent grade water. The recovery ratios for chloride, bromide, and inorganic nitrogen (nitrite plus nitrate) were 72±1, 56±3 and 91±2%, demonstrating the extent of mineralization of the parent compounds. A flow-through reactor was also studied. Higher flow rates and appropriate positioning of the ultrasonic probe accelerated the observed reaction rates. For example, increasing the flow rate from 4.4 to 34 ml min −1 doubled the sonication coefficient for bromobenzene in a mixture, possibly due to better temperature control and mixing. Also, the sonication coefficient was 34% higher for chloropicrin degradation when the probe was positioned 1 cm from the entrance than when the probe was positioned 14.2 cm from the entrance.

Rational interface design of epoxy-organoclay nanocomposites: role of structure-property relationship for silane modifiers.

Montmorillonite was modified by three silane surfactants with different functionalities to investigate the role of surfactant structure on the properties of a final epoxy-organoclay nanocomposite. N-aminopropyldimethylethoxysilane (APDMES), an aminated monofunctional silane, was chosen as a promising surfactant for several reasons: (1) it will bond to silica in montmorillonite, (2) it will bond to epoxide groups, and (3) to overcome difficulties found with trifunctional aminosilane bonding clay layers together and preventing exfoliation. A trifunctional and non-aminated version of APDMES, 3-aminopropyltriethoxysilane (APTES) and n-propyldimethylmethoxysilane (PDMMS), respectively, was also studied to provide comparison to this rationally chosen surfactant. APDMES and APTES were grafted onto montmorillonite in the same amount, while PDMMS was barely grafted (<1 wt%). The gallery spacing of APDMES organoclay was greater than APTES or PDMMS, but the final nanocomposite gallery spacing was not dependent on the surfactant used. Different concentrations of APDMES modified montmorillonite yielded different properties, as concentration decreased glass transition temperature increased, thermal stability increased, and the storage modulus decreased. Storage modulus, glass transition temperature, and thermal stability were more similar for epoxy-organoclay composites modified with the same concentration of silane surfactant, neat epoxy, and epoxy-montmorillonite nanocomposite.

Hydrolysis and H2O2-assisted UV photolysis of 3-chloro-1,2-propanediol

3-Chloro-1,2-propanediol (3-MCPD) is a chlorinated alcohol that is often formed as a by-product in the manufacturing of food products. In addition, 3-MCPD may be a disinfection by-product from wastewater treatment by chlorine and may be present in drinking waters from purification plants using epichlorohydrin-linked cationic polymer resins as flocculants. Due to concerns about the toxicity of 3-MCPD and its potential presence in water samples, the removal of 3-MCPD from water should be addressed and examined. For the first time a systematic examination of the removal of 3-MCPD via hydrolysis and photolysis processes is presented. 3-MCPD is shown to undergo hydrolysis at near neutral pH values, but at much slower rates than can be obtained by UV/H2O2 processes. 3-MCPD does not undergo rapid direct photolysis. Re-evaluation of temperature and pH dependent hydrolysis rate data indicates that hydrolysis is first order with respect to [OH(-)].

The Impact of Particulates on the Aqueous Sonication of Bromobenzene

Sonodegradation of bromobenzene, bromophenolate ion, and 2,4,5-trichlorobiphenyl was studied in the presence of various types of solid particles suspended in water. Three particle diameters (10 nm, 15 microm, and 35 microm) and two particle types (silica particles and organic resin) were investigated over a range of particle concentrations (0.05-10 g l(-1)). The sonochemical decomposition rate constant for bromobenzene (k = 0.044 +/- 7.50 x 10(-4) min(-1) at 20 kHz) was not significantly impacted by very fine silica particles (10 nm). The presence of 15 microm silica decreased sonication rates slightly (<7%) even at a concentration of 10 g l(-1). Organic resin particles demonstrated a more significant impact, particularly at higher concentration and with very hydrophobic compounds. These findings are significant for the application of ultrasound to treatment streams containing solid particles.

Examining the relationship between resistance to change and undergraduate engineering students’ environmental knowledge and attitudes

Engineering professional associations identified environmental sustainability as a key responsibility of the educated engineer. Data from national surveys of the general public demonstrate low environmental knowledge levels and a high level of resistance when it comes to environmental behavior. The purpose of this study was to examine the relationship between first-year engineering students’ environmental knowledge and attitudes and resistance to change (RtC). The authors administered instruments measuring RtC and environmental knowledge and attitudes to three groups (n = 3169) of first-year engineering students in the fall semesters of 2008–2010. Students showed the highest mean scores on the Cognitive Rigidity subscale of RtC. Overall, weak, negative correlations were found between most RtC subscales and environmental knowledge/attitudes, meaning that students with higher RtC score lower overall on environmental knowledge and consider sustainable development less important. Findings can aid researchers and curriculum designers in understanding students’ knowledge levels and the relationship between RtC factors and knowledge/attitudes.