Although it has been
recognized that the interference between heavy
metal ions (HMIs) becomes a severe problem for the simultaneous electroanalysis
of multiple HMIs, the factor leading to the interference is still
difficult to identify, due to the limited understanding of the electroanalytic
kinetics. In this work, a kinetic model is built for the electroanalysis
of HMIs, and the electroanalytic results are simulated for Cd(II),
Cu(II), and their mixture as examples for the interference investigation.
The mutual interference between Cd and Cu is observed on the glassy
carbon electrode. By applying the kinetic model, the replacement of
deposited Cd by Cu(II) at the codeposition stage is regarded as the
main reason for the interference, and the corresponding suggestion
for selecting suitable electrode materials to avoid such interference
is also provided.
The thermal properties of Si1 – xGex alloys are important for two major reasons: one is their applications in high-temperature thermoelectrics and the other is the increasing heat dissipation demand for high power density devices. However, the large lattice mismatch between silicon and germanium leads to tremendous difficulties to obtain high-quality Si1 – xGex thin films, especially when x > 0.5. In this study, we obtained a series of high crystalline quality Si1 – xGex thin films with x covering all the way from 0 to 1 on Si substrates by molecular beam epitaxy. The out-of-plane thermal conductivities of these Si1 – xGex films were measured by the time-domain thermoreflectance approach. Results show that while the thermal conductivity can vary significantly with composition, it only changes marginally in the temperature range of 100 K–300 K for a specific Ge content x. A theoretical analysis indicates that alloy and boundary scatterings are the dominant mechanisms for the thermal transport in these Si1 – xGex (x = 0–1) alloy films.
Significant
progress has been made in nanomaterial-modified
electrodes
for highly efficient electroanalysis of arsenic(III) (As(III)). However,
the modifiers prepared using some physical methods may easily fall
off, and active sites are not uniform, causing the potential instability
of the modified electrode. This work first reports a promising practical
strategy without any modifiers via utilizing only soluble Fe3+ as a trigger to detect trace-level As(III) in natural water. This
method reaches an actual detection limit of 1 ppb on bare glassy carbon
electrodes and a sensitivity of 0.296 μA ppb–1 with excellent stability. Kinetic simulations and experimental evidence
confirm the codeposition mechanism that Fe3+ is preferentially
deposited as Fe0, which are active sites to adsorb As(III)
and H+ on the electrode surface. This facilitates the formation
of AsH3, which could further react with Fe2+ to produce more As0 and Fe0. Meanwhile, the
produced Fe0 can also accelerate the efficient enrichment
of As0. Remarkably, the proposed sensing mechanism is a
general rule for the electroanalysis of As(III) that is triggered
by iron group ions (Fe2+, Fe3+, Co2+, and Ni2+). The interference analysis of coexisting ions
(Cu2+, Zn2+, Al3+, Hg2+, Cd2+, Pb2+, SO4
2–, NO3
–, Cl–, and F–) indicates that only Cu2+, Pb2+, and F– showed inhibitory effects on As(III) due
to the competition of active sites. Surprisingly, adding iron power
effectively eliminates the interference of Cu2+ in natural
water, achieving a higher sensitivity for 1–15 ppb As(III)
(0.487 μA ppb–1). This study provides effective
solutions to overcome the potential instability of modified electrodes
and offers a practical sensing platform for analyzing other heavy-metal
anions.
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