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"Alexander, L. K"
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Graphene/BiVO4/TiO2 nanocomposite: tuning band gap energies for superior photocatalytic activity under visible light
A facile, ultrasonic wave-assisted one pot hydrothermal method has been developed to fabricate reduced graphene oxide/bismuth vanadate/titanium oxide (RGO/BiVO
4
/TiO
2
) ternary nanocomposites. By utilizing graphene oxide (GO) as multifunctional structure, RGO/BiVO
4
/TiO
2
(GBT) with diverse percentage composition possessing varying band gap energies is obtained. XRD and Raman spectroscopy evince formation of tetragonal and monoclinic phases of BiVO
4
. The band gap energies of the components of the composite were determined by applying modified Kubelka–Munk function on UV–Vis DRS data. Tuning of band gap energy of the BiVO
4
and TiO
2
were simultaneously achieved by modifying the concentrations of GO and TiO
2
during synthesis. The GBT exhibited enhanced photocatalytic degradation of methylene blue (MB) under visible light irradiation. The relative photocatalytic activity rates of the composites in GBT series are in agreement with the photoluminescence data. The mechanism behind the activity suggests GO acting as an electron trapper and TiO
2
behaving as an efficient mediating co-catalyst. The band gap energy tuning led to reduction in time needed for complete MB degradation from 40 min with RGO/BiVO
4
to 10 min with the ternary composite GBT. It is expected that the work would encourage new vistas to engineer different combinations of graphene based ternary composites which might lead to potential applications guided by band gap tuning.
Journal Article
Poemhood, our black revival : history, folklore & the Black experience: a young adult poetry anthology
Featuring contributions from an award-winning, bestselling group of Black voices, past and present, this powerful poetry anthology elicits vital conversations about race, belonging, history and faith to highlight Black joy and pain.
Book
Enhanced synergetic effect of Cr(VI) ion removal and anionic dye degradation with superparamagnetic cobalt ferrite meso–macroporous nanospheres
The overall effectiveness of a photocatalytic water treatment method strongly depends on various physicochemical factors. Superparamagnetic photocatalysts have incomparable advantage of easy separation using external magnetic fields. So, the synthesis of efficient superparamagnetic photocatalysts and the development of a deep understanding of the factors influencing their catalytic performances are important. CoxZn1−xFe2O4 (x = 0, 0.5, 1) ferrite nanospheres were synthesized by the solvothermal route. The reduction of Cr(VI) and degradation of methyl orange (MO) impurities were carried out in single- and binary-component system under visible light irradiation. The adsorption experiments were done by the catalyst in the water solution containing the impurities. The magnetic and optical properties were studied by VSM and UV–Vis analysis. The nature of porosity was investigated using the BET method. 3D nanospheres of diameter about 5–10 nm were fabricated. The binary-contaminant system exhibited synergetic photocatalytic effect (80% improvement in activity rate) against the nanoparticles. The corresponding mechanism is discussed. CoFe2O4 exhibited better adsorption, photocatalytic and magnetic separation efficiency due to its higher surface area (50% higher), narrower band gap (25% lesser), smaller crystallite size, a strong magnetic strength (51.35 emu/g) and meso–macro hierarchical porous structure. The adsorption of Cr(VI) and MO can be approximated to the Langmuir and Freundlich model, respectively.
Journal Article
From first grade forward: Early foundations of High School dropout
In tracking the educational progress of a sample of Baltimore school- children from entrance into first grade fall 1982 through early spring 1996, the authors examined the children's personal qualities, first-grade experiences, and family circumstances as precursors to high school dropout. Logistic regression analyses were used to identify predictors of dropout involving family context measures (stressful family changes, parents' attitudes, and parents' socialization practices), children's personal resources (attitudes and behaviors), and school experiences ( test scores, marks, and track placements). These various measures were found to influence dropout independently of sociodemographic factors and account for much of the difference in the odds of dropout associated with family socioeconomic status, gender, family type, and other \"risk factors.\" The authors take a life-course perspective on dropout, viewing it as the culmination of a long-term process of academic disengagement.(DIPF/Abstract übernommen)
Journal Article
Graphene/BiVO.sub.4/TiO.sub.2 nanocomposite: tuning band gap energies for superior photocatalytic activity under visible light
A facile, ultrasonic wave-assisted one pot hydrothermal method has been developed to fabricate reduced graphene oxide/bismuth vanadate/titanium oxide (RGO/BiVO.sub.4/TiO.sub.2) ternary nanocomposites. By utilizing graphene oxide (GO) as multifunctional structure, RGO/BiVO.sub.4/TiO.sub.2 (GBT) with diverse percentage composition possessing varying band gap energies is obtained. XRD and Raman spectroscopy evince formation of tetragonal and monoclinic phases of BiVO.sub.4. The band gap energies of the components of the composite were determined by applying modified Kubelka-Munk function on UV-Vis DRS data. Tuning of band gap energy of the BiVO.sub.4 and TiO.sub.2 were simultaneously achieved by modifying the concentrations of GO and TiO.sub.2 during synthesis. The GBT exhibited enhanced photocatalytic degradation of methylene blue (MB) under visible light irradiation. The relative photocatalytic activity rates of the composites in GBT series are in agreement with the photoluminescence data. The mechanism behind the activity suggests GO acting as an electron trapper and TiO.sub.2 behaving as an efficient mediating co-catalyst. The band gap energy tuning led to reduction in time needed for complete MB degradation from 40 min with RGO/BiVO.sub.4 to 10 min with the ternary composite GBT. It is expected that the work would encourage new vistas to engineer different combinations of graphene based ternary composites which might lead to potential applications guided by band gap tuning.
Journal Article
The Gender Gap in Math: Its Possible Origins in Neighborhood Effects
Gender differences in most cognitive skills are fading, but a gender gap remains in secondary school that favors males in higher level math skills. This gap is not evident in elementary school where test scores for the two sexes are equivalent. However, the daily experiences of young boys and girls differ in ways that could affect their math skills in early adolescence. In a large random sample of youngsters in Baltimore, over their first two years of school, boys' gains in math reasoning achievement were more sensitive to resources outside the home than were girls'. In line with the greater responsiveness of boys' math skills to these neighborhood resources, the boys' math reasoning scores became significantly more variable over time than did the girls'. When differentiated course programs became available in middle school, this greater variability of the boys' math scores led the high-scoring boys in the \"academic\" program to outscore the girls in that program, even though in the total sample the means for boys and girls were about the same. In short, by the end of middle school a \"gender gap\" emerged in math among high-scoring youngsters. These trends in variability and the greater sensitivity of males to neighborhood resources combined with school tracking offer a new and more sociological perspective on the emergence of the gender gap in math in early adolescence.
Journal Article
Public Schools and the Public Good
Criticism of the public schools in recent years has been both broad-based and unrelenting, yet I argue in this essay that the decline in public education is exaggerated and the accomplishments of public education neglected. Verbal and quantitative achievement levels among school-age youth at present are about where they were in the late fifties through the early sixties, before the purported decline, while disparities across social lines, especially involving minority-majority comparisons, actually are smaller now - much smaller - than they were then. How are we to comprehend these favorable patterns? I argue that improved conditions outside school are an unlikely candidate, but that conditions of schooling, including expenditures, class size, and curricular patterns, have been changing in ways that should boost achievement. My conclusion: despite many \"external\" forces pulling against their successes, not the least being an increasingly hostile political climate, our public schools have been doing a better job than most people realize. My concluding remarks address prospects for further school improvement in light of currently popular reform models, including so-called \"consumer-choice\" and the Charter School movement.
Journal Article
Tracking and Transitions through the Middle Grades: Channeling Educational Trajectories
Using longitudinal data from the Beginning School Study (BSS), the study reported here examined sources of influence on inner-city students' initial middle school placements in English and mathematics and continuity and change in placements through the end of middle school. The study found that test scores and prior retention in grade exert strong effects at the transition into middle school, but so do social background and parents' educational expectations, particularly for higher-level placements. Stability in middle school placements is strong, and neither social background nor educational expectations consistently influences eighth-grade course levels, net of sixth-grade placements and other predictors in the model. The authors conclude that educational trajectories are not grounded in academic considerations alone, but the contributions of nonacademic factors on track placements toward the end of middle school are obscured if the determinants of earlier placements are not included in the model.
Journal Article
When Expectations Work: Race and Socioeconomic Differences in School Performance
Why are expectations for future performance realized more often by some people than by others, and why are such differences in the efficacy of performance expectations socially patterned? We hypothesize that differences in attentiveness to performance feedback may be relevant, reasoning that follow-through behaviors will be less well conceived when expectations are formed without regard to evaluation of previous performance. Using data from Baltimore fourth-grade students and their parents, we find that expectations anticipate marks more accurately when recall of prior marks is correct than when it is incorrect. Because errors of recall (mostly on the high side) are more common among lower-SES and minority children and their parents, their school performance is affected most strongly. Research on school attainment process from a motivational perspective must give more attention to the additional resources that facilitate successful goal attainment, given high expectations. Our perspective focuses on resources internal to the individual, but external constraints also are important. The discussion stresses the need for further work in both areas.
Journal Article