What content is being taught in Introductory Statistics?: Results of nationwide survey

Introductory Statistics is a course commonly taken by students from a variety of wide-ranging majors, sometimes across departments; however, there is little known about the extent topics are covered generally across courses. Textbooks include more material than can reasonably be covered in a single course, but the non-linear nature of many topics means that from course to course the covered content can diverge greatly. We provide results of a nationwide survey of 148 introductory statistics instructors and assess how often concepts are covered in introductory courses across instructor experience, course audience and course pedagogy.Accepted manuscrip

Investigating instructional strategies in introductory statistics

Recommendations for the teaching and learning of introductory statistics at the tertiary level have been set forth by the research community, including recommendations outlining desirable pedagogical strategies such as the use of student-centered instruction and the integration of technology and resampling methods to support the development of students’ conceptual understanding. Yet, surprisingly little is known about how introductory statistics is being taught at colleges and universities across the United States. The research presented here aims to shed light on these aspects of the introductory statistics course by reporting preliminary findings from an instructor survey that was recently completed by 148 instructors nationwide.Accepted manuscrip

Recycled PETg embedded with graphene, multi-walled carbon nanotubes and carbon black for high-performance conductive additive manufacturing feedstock

The first report of conductive recycled polyethylene terephthalate glycol (rPETg) for additive manufacturing and electrochemical applications is reported herein. Graphene nanoplatelets (GNP), multi-walled carbon nanotubes (MWCNT) and carbon black (CB) were embedded within a recycled feedstock to produce a filament with lower resistance than commercially available conductive polylactic acid (PLA). In addition to electrical conductivity, the rPETg was able to hold >10 wt% more conductive filler without the use of a plasticiser, showed enhanced temperature stability, had a higher modulus, improved chemical resistance, lowered levels of solution ingress, and could be sterilised in ethanol. Using a mix of carbon materials CB/MWCNT/GNP (25/2.5/2.5 wt%) the electrochemical performance of the rPETg filament was significantly enhanced, providing a heterogenous electrochemical rate constant, k0, equating to 0.88 (±0.01) × 10−3 cm s−1 compared to 0.46 (±0.02) × 10−3 cm s−1 for commercial conductive PLA. This work presents a paradigm shift within the use of additive manufacturing and electrochemistry, allowing the production of electrodes with enhanced electrical, chemical and mechanical properties, whilst improving the sustainability of the production through the use of recycled feedstock

Additive manufacturing of a portable electrochemical sensor with a recycled conductive filament for the detection of atropine in spiked drink samples

Additive manufacturing (three-dimensional (3D) printing) has promising features for fast prototyping electrochemical systems, from cells to sensors. Conductive filaments containing carbon black and poly(lactic acid) (CB/PLA) for electrode fabrication are commercially available but usually rely on low carbon content, resulting in poor electrochemical properties. Filament fabrication can be done within the laboratory by exploring different materials according to the desired applications. In this work, recycled PLA was used as the thermoplastic base polymer, alongside CB as the conductive filler, and tris (2-ethylhexyl) trimellitate was introduced into the filament matrix as a plasticizer (CB/PLA/TTM) to fabricate additively manufactured electrodes (AMEs). This enhanced the electrochemical properties toward different redox probes and the forensic target atropine. Thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS) were used to characterize the filament and AMEs before and after activation. Additive manufacturing has also been used to develop different cell configurations, which is equally important for good electroanalytical performance. Flow analytical techniques, such as batch-injection analysis (BIA), can be used as an alternative to stationary measurements to enhancing sensitivity and detection limits (LOD) via increasing the mass transport of analytes to the electrochemical platform surface, providing automation and high sample throughput. In this context, we developed a compact (∼5 mL capacity) and versatile additively manufactured BIA cell that can either perform static or hydrodynamic analyses by simply placing a lid on the device with a hole for the BIA pipette tip. Moreover, knowing that forensic chemistry necessitates portable analytical tools to help police investigation at the crime scene, the AM-BIA cell and the bespoke AMEs were coupled to a portable electrochemical apparatus for on-site atropine analysis in adulterated beverage samples. Atropine determination was performed by differential pulse voltammetry (DPV) and amperometry (BIA-AMP) in the same cell, presenting good repeatability for both methods (6% RSD). As expected, the BIA-AMP method showed higher sensitivity (0.0783 μA μM–1) and lower LOD (0.51 μM) compared to the stationary DPV method (sensitivity: 0.0148 μA μmol–1 L; LOD: 2.60 μM); they both presented good recovery values, varying from 102 to 109% for two spiked samples of gin and whisky. Thus, the versatility and portability of the developed AM-BIA cell coupled with the bespoke filament CB/PLA/TTM allow for rapid and accurate screening and quantification of atropine in real forensic scenarios

Utilising bio-based plasticiser castor oil and recycled PLA for the production of conductive additive manufacturing feedstock and detection of bisphenol A

The production of electrically conductive additive manufacturing feedstocks from recycled poly(lactic acid) (rPLA), carbon black (CB), and bio-based plasticiser castor oil is reported herein. The filament was used to print additively manufactured electrodes (AMEs), which were electrochemically benchmarked against geometrically identical AMEs printed from a commercially available conductive filament. The castor oil/rPLA AMEs produced an enhanced heterogeneous electrochemical rate constant of (1.71 ± 0.22) × 10−3 cm s−1 compared to (0.30 ± 0.03) × 10−3 cm s−1 for the commercial AME, highlighting the improved performance of this filament for the production of working electrodes. A bespoke electroanalytical cell was designed and utilised to detect bisphenol A (BPA). The AMEs made from the castor oil/rPLA gave an enhanced electroanalytical performance compared to the commercial filament, producing a sensitivity of 0.59 μA μM−1, a LOD of 0.10 μM and LOQ of 0.34 μM. This system was then successfully applied to detect BPA in spiked bottled and tap water samples, producing recoveries between 89-104%. This work shows how the production of conductive filaments may be done more sustainably while improving performance

Recycled additive manufacturing feedstocks for fabricating high voltage, low-cost aqueous supercapacitors

The first recycled conductive poly(lactic acid) (PLA) filament derived from post-industrial waste sources for additive manufacturing (AM) is reported herein, presenting a paradigm shift in plastic waste recycling, AM filament production, and AM energy storage architectures. Filaments utilizing a base of recycled PLA, carbon black (CB) as a conductive filler, and polyethylene glycol (PEG) as a plasticizer are used to produce aqueous AM symmetric supercapacitor platforms that can reach capacitance values 75 times higher than commercially available conductive PLA filaments. Furthermore, through the rapid prototyping capabilities of AM and GCode modification, it is seen that changing the electrode architecture from solid to a mesh with additional inter-layer spacing is able to further enhance electrode performance by 3.5 times due to improvements in the surface area, ion accommodating capabilities and faster ion diffusion. The symmetric full cell device is capable of delivering 7.82 mF cm−2, 4.82 µWh cm−2, and 433.32 µW cm−2 of capacitance, energy, and power density, respectively. Moreover, the material cost is £0.15 per electrode. This work represents a new direction for plastic waste recycling, in which low-value recycled base products can be manufactured into high-value end products in their second cycles

Circular economy electrochemistry: recycling old mixed material additively manufactured sensors into new electroanalytical sensing platforms

Recycling used mixed material additively manufactured electroanalytical sensors into new 3D-printing filaments (both conductive and non-conductive) for the production of new sensors is reported herein. Additively manufactured (3D-printed) sensing platforms were transformed into a non-conductive filament for fused filament fabrication through four different methodologies (granulation, ball-milling, solvent mixing, and thermal mixing) with thermal mixing producing the best quality filament, as evidenced by the improved dispersion of fillers throughout the composite. Utilizing this thermal mixing methodology, and without supplementation with the virgin polymer, the filament was able to be cycled twice before failure. This was then used to process old sensors into an electrically conductive filament through the addition of carbon black into the thermal mixing process. Both recycled filaments (conductive and non-conductive) were utilized to produce a new electroanalytical sensing platform, which was tested for the cell's original application of acetaminophen determination. The fully recycled cell matched the electrochemical and electroanalytical performance of the original sensing platform, achieving a sensitivity of 22.4 ± 0.2 μA μM-1, a limit of detection of 3.2 ± 0.8 μM, and a recovery value of 95 ± 5% when tested using a real pharmaceutical sample. This study represents a paradigm shift in how sustainability and recycling can be utilized within additively manufactured electrochemistry toward promoting circular economy electrochemistry

Circular economy electrochemistry: creating additive manufacturing feedstocks for caffeine detection from post-industrial coffee pod waste

The recycling of post-industrial waste poly(lactic acid) (PI-PLA) from coffee machine pods into electroanalytical sensors for the detection of caffeine in real tea and coffee samples is reported herein. The PI-PLA is transformed into both nonconductive and conductive filaments to produce full electroanalytical cells, including additively manufactured electrodes (AMEs). The electroanalytical cell was designed utilizing separate prints for the cell body and electrodes to increase the recyclability of the system. The cell body made from nonconductive filament was able to be recycled three times before the feedstock-induced print failure. Three bespoke formulations of conductive filament were produced, with the PI-PLA (61.62 wt %), carbon black (CB, 29.60 wt %), and poly(ethylene succinate) (PES, 8.78 wt %) chosen as the most suitable for use due to its equivalent electrochemical performance, lower material cost, and improved thermal stability compared to the filaments with higher PES loading and ability to be printable. It was shown that this system could detect caffeine with a sensitivity of 0.055 ± 0.001 μA μM–1, a limit of detection of 0.23 μM, a limit of quantification of 0.76 μM, and a relative standard deviation of 3.14% after activation. Interestingly, the nonactivated 8.78% PES electrodes produced significantly better results in this regard than the activated commercial filament toward the detection of caffeine. The activated 8.78% PES electrode was shown to be able to detect the caffeine content in real and spiked Earl Grey tea and Arabica coffee samples with excellent recoveries (96.7–102%). This work reports a paradigm shift in the way AM, electrochemical research, and sustainability can synergize and feed into part of a circular economy, akin to a circular economy electrochemistry

Recycled additive manufacturing feedstocks with carboxylated multi-walled carbon nanotubes toward the detection of yellow fever virus cDNA

Recycled additive manufacturing sensing platforms are fabricated with carboxylated multi-walled carbon nanotubes (COOH-MWCNT) with exhibit enhanced electrochemical biosensor performance allowing for the enhanced direct coupling of the biorecognition element to the COOH-MWCNT for the preparation of an electrochemical genosensor for the detection of yellow fever virus cDNA. Bespoke additive manufacturing filaments was produced using recycled poly(lactic acid) (rPLA, 65 wt%), polyethylene succinate (PES, 10 wt%), carbon black (CB, 15 wt%), and COOH-MWCNT (10 wt%) which exhibits enhanced electrochemical performance over that of commercial filament. A bespoke all-in-one additive manufactured electroanalytical cell is proposed, with the working, reference and counter electrodes in addition to a modification rim that allows for the facile production of biosensors through the application of droplets. The genosensor was applied to the detection of yellow fever Virus cDNA using anodic square wave voltammetry; a linear dynamic range (LDR) of 0.5–15 µM with an R2 of 0.9995, sensitivity of 177 ± 2 µA µM−1, limit of detection (LOD) of 0.138 µM, and limit of quantification (LOQ) of 0.859 µM were obtained. This work highlights how bespoke additive manufacturing filament production can enhance biosensing platforms, whilst using recycled feedstock to improve end-product sustainability