Pedro J. J. Alvarez

Bio: Pedro J. J. Alvarez is an academic researcher from Rice University. The author has contributed to research in topics: Bioremediation & Medicine. The author has an hindex of 89, co-authored 378 publications receiving 34837 citations. Previous affiliations of Pedro J. J. Alvarez include University of Minnesota & University of Michigan.

Chemistry and microbiology of permeable reactive barriers for in situ groundwater clean up.

Abstract: Permeable reactive barriers (PRBs) are receiving a great deal of attention as an innovative, cost-effective technology for in situ clean up of groundwater contamination. A wide variety of materials are being proposed for use in PRBs, including zero-valent metals (e.g., iron metal), humic materials, oxides, surfactant-modified zeolites (SMZs), and oxygen- and nitrate-releasing compounds. PRB materials remove dissolved groundwater contaminants by immobilization within the barrier or transformation to less harmful products. The primary removal processes include: (1) sorption and precipitation, (2) chemical reaction, and (3) biologically mediated reactions. This article presents an overview of the mechanisms and factors controlling these individual processes and discusses the implications for the feasibility and long-term effectiveness of PRB technologies.

Mechanisms of photochemistry and reactive oxygen production by fullerene suspensions in water.

Abstract: Buckminsterfullerene (C60) is a known photosensitizer that produces reactive oxygen species (ROS) in the presence of light; however, its properties in aqueous environments are still not well understood or modeled. In this study, production of both singlet oxygen and superoxide by UV photosensitization of colloidal aggregates of C60 in water was measured by two distinct methods: electron paramagnetic resonance (EPR) with a spin trapping compound, and spectrophotometric detection of the reduced form of the tetrazolium compound XTT. Both singlet oxygen and superoxide were generated by fullerol suspensions while neither was detected in the aqu/nC60 suspensions. A mechanistic framework for photosensitization that takes into account differences in C60 aggregate structure in water is proposed to explain these results. While theory developed for single molecules suggests that alterations to the C60 cage should reduce the quantum yield for the triplet state and associated ROS production, the failure to detect ROS production by aqu/nC60 is explained in part by a more dense aggregate structure compared with the hydroxylated C60.

Impacts of silver nanoparticles on cellular and transcriptional activity of nitrogen-cycling bacteria

Abstract: The widespread use of silver nanoparticles (AgNPs) raises the potential for environmental releases that could impact microbial ecosystem services. In the present study, the authors address how the AgNPs and Ag+ that they release may impact nitrogen-cycling bacteria. The authors studied the cellular and transcriptional response of the denitrifier Pseudomonas stutzeri, the nitrogen fixer Azotobacter vinelandii, and the nitrifier Nitrosomonas europaea exposed to 35 nm (carbon-coated) AgNPs or to Ag+ (added as AgNO3). Based on minimum inhibitory concentrations (MICs), Ag+ was 20 times to 48 times more toxic to the tested strains than AgNPs (including Ag+ released during exposure). Exposure to sublethal concentrations of AgNPs or Ag+ (representing 10% of the respective MIC for AgNO3) resulted in no significant effect on the expression of the denitrifying genes narG, napB, nirH, and norB in P. stutzeri or the nitrogen-fixing genes nifD, nifH, vnfD, and anfD in A. vinelandii, whereas nitrifying genes (amoA1 and amoC2) in N. europaea were upregulated (2.1- to 3.3-fold). This stimulatory effect disappeared at higher silver concentrations (60% of the Ag+ MIC), and toxicity was exerted at concentrations higher than 60% of the Ag+ MIC. The MIC for N. europaea was 8 times to 24 times lower than for the other strains, indicating higher susceptibility to AgNPs. This was corroborated by the lower half-lethal concentration for N. europaea (87 µg/L) compared with P. stutzeri (124 µg/L) and A. vinelandii (>250 µg/L) when cells were exposed with Ag+ for 24 h in 1 mM bicarbonate buffer. This suggests that ammonia oxidation would be the most vulnerable nitrogen-cycling process in wastewater treatment plants receiving AgNPs and in agricultural soils amended with biosolids that concentrate them. Environ Toxicol Chem 2013;32:1488–1494. © 2013 SETAC

Graphitic Carbon Nitride (g-C3N4)-Based Photocatalysts for Artificial Photosynthesis and Environmental Remediation: Are We a Step Closer To Achieving Sustainability?

Abstract: As a fascinating conjugated polymer, graphitic carbon nitride (g-C3N4) has become a new research hotspot and drawn broad interdisciplinary attention as a metal-free and visible-light-responsive photocatalyst in the arena of solar energy conversion and environmental remediation. This is due to its appealing electronic band structure, high physicochemical stability, and “earth-abundant” nature. This critical review summarizes a panorama of the latest progress related to the design and construction of pristine g-C3N4 and g-C3N4-based nanocomposites, including (1) nanoarchitecture design of bare g-C3N4, such as hard and soft templating approaches, supramolecular preorganization assembly, exfoliation, and template-free synthesis routes, (2) functionalization of g-C3N4 at an atomic level (elemental doping) and molecular level (copolymerization), and (3) modification of g-C3N4 with well-matched energy levels of another semiconductor or a metal as a cocatalyst to form heterojunction nanostructures. The constructi...

Advanced Oxidation Processes for Organic Contaminant Destruction Based on the Fenton Reaction and Related Chemistry

Abstract: Fenton chemistry encompasses reactions of hydrogen peroxide in the presence of iron to generate highly reactive species such as the hydroxyl radical and possibly others. In this review, the complex mechanisms of Fenton and Fenton-like reactions and the important factors influencing these reactions, from both a fundamental and practical perspective, in applications to water and soil treatment, are discussed. The review covers modified versions including the photoassisted Fenton reaction, use of chelated iron, electro-Fenton reactions, and Fenton reactions using heterogeneous catalysts. Sections are devoted to nonclassical pathways, by-products, kinetics and process modeling, experimental design methodology, soil and aquifer treatment, use of Fenton in combination with other advanced oxidation processes or biodegradation, economic comparison with other advanced oxidation processes, and case studies.