Building an inverted peak voltage detector
With 0 and 9 V rails, LM741 will only work for input voltages between something like +4 and +5 V. Maybe try this with an ideal op-amp first, then find a better choice than LM741 to get a reasonable common mode input range.
The way your diode is oriented, you've made a positive peak detector, not a negative peak detector. Try reversing the diode orientation.